Title: Article type: Original Research Article

Title: Effect of invasion by Hyptis suaveolens on plant diversity and selected soil properties of a constructed tropical grassland

Article type: Original Research Article

© The Author 2017. Published by Oxford University Press on behalf of the Institute of Botany, Chinese Academy of Sciences and the Botanical Society of China. All rights reserved. For permissions, please email: [email protected] Downloaded from https://academic.oup.com/jpe/article-abstract/doi/10.1093/jpe/rtx045/4085044/Effect-of-invasion-by-Hyptis-suaveolens-on-plant by Banaras Hindu University user on 04 October 2017

Authors name and affiliations: Talat Afreen, Pratap Srivastava, Hema Singh*, Jamuna Sharan Singh Ecosystems Analysis Laboratory, Department of Botany, Institute of Science, Banaras Hindu University, Varanasi 221005, India Corresponding author email: [email protected]

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Abstract: Aims Hyptis suaveolens (L.) Poit is an important invader of the tropical and sub-tropical regions of the world. In our study, it has been investigated that how does the H. suaveolens invasion regulate plant species diversity across the seasons in the dry tropical grassland. We hypothesized that a shift in soil inorganic-N availability is caused by invasion, and this shift is integral to access the invasion effect on plant diversity. Methods The study was performed in experimental plots at the Botanical Garden of the Banaras Hindu University (25°16’3.3” N and 82°59’22.7” E), Varanasi, Uttar Pradesh, India. Five replicates (each, 2m x 2m) of non-invaded grassland plots (NIG) and five grassland plots invaded with H. suaveolens (IG) were established. These plots were constructed by transplanting indigenous grassland patches from an adjacent native grassland. In the invaded plots 20 individuals of H. suaveolens were transplanted per plot. After one year of establishment, diversity attributes and soil properties were recorded from these plots in three seasons as per standard protocol. Important findings The results indicated that Hyptis invasion negatively affects plant diversity, with relatively higher impact in rainy season as compared to the winter season. IG exhibited lower soil moisture content and temperature than NIG in rainy season, whereas soil ammoniumN, nitrate-N, total inorganic-N, N mineralization registered higher values for IG than NIG in both rainy and winter season. Diversity indices were negatively correlated with soil inorganic-N pool and N mineralization. However, these indices were positively correlated with microbial biomass carbon (MBC), and the correlation coefficient for this relationship was higher for rainy season as compared to winter. Species richness (r = 0.65) and Shannon diversity (r = 0.757) were 3


significantly correlated with the ratio of ammonium-N to nitrate-N. The negative effect of invasion by Hyptis suaveolens on the plant diversity is possibly mediated by the effect of invasion on N- mineralization processes (mainly nitrification) and the availability of soil inorganic-N pools. The study indicates that Hyptis invasion has an enormous potential to change the structure and composition of plant communities in the dry tropical grasslands. Key words: Dry Tropical Grassland; Diversity; Hyptis suaveolens; Mineralization; Soil Ammonium to Nitrate Ratio

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1. Introduction: Invasion is considered the second to habitat destruction in affecting global biodiversity (Simberloff 1995, Simberloff et al. 2013). The invasive species spread rapidly in the new habitats (Padalia et al. 2015), and affect biodiversity, productivity and species composition of the invaded ecosystems (Hulme et al. 2013). The plasticity of germination related traits of the alien species assist in their establishment in any ecosystem (Wainwright et al. 2013). These attributes allow them to adapt to various habitats or to the changing environment and help in initiating their growth earlier than the native species. It is well known that the establishment of alien species affects the ecological functioning of all ecosystems (Vilà et al. 2011). Hyptis suaveolens (L.) Poit, which is commonly known as Bushmint or pignut, is an important invader of the tropical and sub-tropical regions of the world (Wulff and Medina 1971, Sarmiento 1984,, Afolayan 1993). Its invasion has been reported from different parts of India (Wealth of India 1959, Yoganarasimhan 2000, Sharma et al. 2009). The species prefers wet and warm areas for growth and spread (Padalia et al. 2014). The aboveground parts dry up and wither away in the summer season but plants vigorously resprout at the beginning of the subsequent rainy season. The growth of Hyptis is intense and it rapidly covers extensive areas after the rains. The small seed size and seed dimorphism (Schwarzkopf et al. 2009) support its growth in different microsites and in different temperature conditions, respectively (Maia 2008). Hyptis possesses several characteristics common to other invasive species, such as lack of natural enemies (Julien, 2002) and the presence of allelochemicals (Kapoor 2011, Chatiyanon et al. 2012, Islam and Kato-Noguchi 2013, Joseph and Jeeva 2016), that help in its survival and spread.

Raizada (2006) has argued that this species has wide ecological amplitude, high

plasticity and reproductive capacity because of which it is able to grow on a variety of soil types, 5


land uses and land cover type, as also suggested by Padalia et al. (2013). Hyptis possesses attributes such as faster growth rate than native species, massive seed production (>2000 m-2), high proliferation rate, dual mode of reproduction (from perennating root-stocks as well as seed) and higher resistance against pathogens due to allelo-chemicals and essential oil (Raizada 2006). Grassland represents one of the world’s most widespread vegetation types covering about 26% of the earth’s land surface (Boval and Dixon 2012). It contains about 20% of the total global pool of soil C (Ramankutty et al. 2008, FAOSTAT 2009), and therefore holds crucial importance in global climate change. Grassland is of immense importance as it (1) supports many plants of medicinal importance, (2) is efficient in absorbing rainwater and (3) plays a vital role in water retention, hydrology and nutrient cycling (Conant et al. 2001, Boval and Dixon 2012). H. suaveolens is rapidly invading the grasslands of the dry tropical region of India (Raizada 2006, Padalia et al. 2013). Invasive species, in general, modify soil nutrient pools and processes by altering litter quality (Weidenhamer and Callaway 2010, Ricciardi et al. 2013), composition of soil microbial community (Kourtev et al. 2002, Batten et al. 2005, Putten et al. 2013, Maron et al. 2014), rates of C and N mineralization, potential nitrification (Haubensak and Parker 2004, Parker and Schimel 2010), soil moisture (Blank and Morgan 2014, Nielsen et al. 2014), soil pH (Sharma et al. 2009), energy flux and soil temperature (Prater and DeLucia 2006, Kuester et al. 2014). Some invasive species are reported to increase N-availability in soil ecosystem through changed community structure and metabolic activities of soil microorganisms (Dassonville et al. 2011, Hawkes et al. 2005). The invasive species change the quantity or quality of litter, either by shedding more leaves with slow decomposition rate (Center et al. 2012) or by depositing N rich 6


litter having higher decomposition rate as compared to native species. It is reported that the invading species alter the soil microbial community (Xiao et al. 2014) such that the altered community favors the invader species (Raizada et al. 2008). Thus, invasion changes the ecosystem dynamics, stability, productivity, nutrient balance, and other aspects of ecosystem functioning, primarily affecting soil microbial activity. The impact of invasion by Hyptis suaveolens on the invaded habitat is, however, not known. This study aims to address the question as to how H. suaveolens invasion regulates plant species diversity across the seasons in the dry tropical grassland. We hypothesized that a qualitative shift in soil inorganic-N availability is caused by invasion, and this shift is integral to the invasion effect on plant diversity. Three objectives were formulated for testing this hypothesis: (1) to study the diversity indices in Hyptis invaded and non-invaded grassland plots across seasons, (2) to study the availability of soil inorganic-N pools and associated microbial processes, (3) to investigate how do the soil properties, particularly the inorganic-N availability, relate with plant diversity.

2. Materials and methods 2.1. Study sites The study was performed in the experimental plots of the Botanical Garden of the Banaras Hindu University (25°16’3.3” N and 82°59’22.7” E), Varanasi, Uttar Pradesh, India. The area is a part of middle Indo-Gangetic plains, located approximately 86.7 m above the mean sea level. The climatic conditions are shown in supplementary figure 1. Climate is monsoonal with annual rainfall of about 1100 mm, of which 80% is received between June and September. The 7


year is characterized by three seasons, viz., a hot summer (April to June), a warm rainy season (July to September), and a cold winter (November to February). The months of March and October constitute the transition periods, between winter and summer, and between rainy and winter seasons, respectively. The mean monthly temperature ranges from a minimum of 13.76 °C during winter to a maximum of 35.22 °C during the summer season. The locality thus, experiences a strong seasonality making the rainy season as the grand growth period for plants and the summer season as the most hostile to plant growth. The soil is deep, pale brown in color and silty loam in texture, and is characterized as inceptisol. 2.2. Experimental design Before establishment of the treatment plots, we had ploughed the whole field and the soil was properly homogenized and analyzed. The initial soil physiochemical properties are included in Table 1. Each treatment was established with 5 replicates in 2014. Grassland plots were prepared by transplanting indigenous grassland patches from an adjacent native grassland. Ten plots, each of 2 x 2m size were demarcated, each pair of plots was separated from each other by a 1 m wide strip. Five of these plots were randomly allocated to NIG and the other five to IG treatment. In each of the IG plots, H. suaveolens was established by randomly transplanting 20 seedlings. Thus the size of each replicate plot was 2 m x 2 m. After establishment, the plots were allowed to rest for one full annual cycle, and then soil was sampled during the peak of each of the three seasons, i.e. in the months of January (winter), June (summer) and September (rainy), and the vegetation was sampled in rainy and winter seasons in the second year. 2.3. Soil sampling

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Soil was sampled from five random locations from 0-10 cm depth using a soil corer, from each plot, and the soil samples collected from the five locations were pooled for each replicate plot. The sampling was done in each of the three seasons. These samples were sieved using a 2 mm mesh screen and stored at 4ºC for analysis. Soil moisture was estimated by gravimetric method. Soil temperature was measured by Li-Cor temperature probe (LI-6400-09, LI-COR Inc., Lincoln NE, USA). The soil pH was determined by digital pH meter (model 702 SM Titrino, Metrohm Ltd. Switzerland), using soil: solution ratio of 1:2.5. Total N (TN) was estimated using Kjeldahl method (Jackson 1958). Phenol-disulphonic acid method (Jackson 1958), and phenate method (APHA 1985) were used for the determination of nitrate-N and ammonium-N, respectively. Microbial biomass was measured by chloroform fumigation-extraction method (Brookes et al. 1985; Vance et al. 1987). N mineralization rate was estimated by using buried bag technique (Eno 1960). 2.4. Vegetation sampling

In each 2 m x 2 m plot, one 1 m x 1 m quadrat was demarcated in the center, and this quadrat was divided into four 50 cm x 50 cm sub-quadrats as working units for the vegetation sampling. In each sub-quadrat, species data (i.e. name and numbers) were recorded. The collected plant species were categorized on the basis of their status (i.e. native or invasive), growth form (i.e. grass or forb), life span (annual or perennial) and family. Importance Value Index (IVI) of each species for each plot was calculated on the basis of relative density, relative frequency and relative abundance (Curtis and Mcintosh 1951) according to the following formulae: IVI = RF + RD + RA Where, RF, relative frequency = 100 × (number of quadrats of occurrence of species A / number of quadrats of occurrence of all species) ; RD, relative density = 100 × (number of individuals of 9


species A / total number of individuals of all species); RA, relative abundance = 100 × (abundance of the species / total abundance of all species), where Abundance = total number of individuals of species A / number of quadrats in which species A occurred. The data were presented on per meter square basis. Species richness (SR) was evaluated as number of species per square meter, evenness (EW) and alpha diversity were calculated by using the following equations: EW = S-1/ln ni – ln s (Whittaker 1972) s

H    pi ln pi (Shannon and Weaver 1949) i 1

In the above equations, S = number of species; ni = number of most important species; s = number of least important species; pi = proportion of importance value belonging to species ‘i’; H′ = Shannon index of diversity. 2.5. Statistical analysis

Data were subjected to Analysis of Variance (ANOVA) to determine the effect of invasion on the soil properties and plant diversity of the grassland. Data were also subjected to correlation analysis to observe the relationship among soil properties, and between soil properties and diversity indices. The plots were ordinated by Principal Component Analysis (PCA) using PCORD software (McCune and Mefford 1999) using IVI data for plant species composition and soil inorganic-N content. It was done to identify the effect of invasion on species composition as well as the effect of species composition on soil inorganic-N content and associated microbial processes across the seasons. Moreover, the relationship of H. suaveolens abundance (on the basis of IVI) with PCA axes scores was determined. Statistical analysis was done using SPSS (SPSS Inc. Version 16). 10


3. Results 3.1. Soil properties Our results indicate significant impact of Hyptis invasion on all soil properties (Supplementary Table 1). Except for pH, season had significant influence on all soil properties. Among all treatment x season interactions only that for pH was not significant, all other were statistically significant (Supplementary Table 1). Soil moisture was found higher in NIG compared to IG in all seasons (Fig. 1) Soil moisture exhibited significant positive correlation with soil ammoniumN to nitrate ratio (r = 0.88, P < 0.01) and soil microbial biomass carbon (MBC) (r = 0.93, P < 0.01). Soil temperature also differed among the vegetated plots, NIG showing significantly higher value of soil temperature than IG in the winter and rainy seasons (Fig. 1). Soil pH was also affected by treatment (i.e, invasion) (Supplementary Table 1). IG exhibited a lower soil pH than NIG (Fig. 1). Total soil inorganic-N content (i.e. ammonium-N plus nitrate-N) was higher in IG than NIG (Fig. 1). MBC was lower in IG than NIG (Fig. 1), and showed an inverse relationship with N mineralization across the seasons (Supplementary table 2). N mineralization varied strongly between seasons and was higher in rainy season followed by winter and summer season, and was significantly higher in IG than NIG (Fig. 2). N mineralization was negatively correlated with soil ammonium-N content and nitrate-N content, in winter and summer seasons (Supplementary Table 2) but was positively correlated with the ammonium- and nitrate-N in the rainy season (r = 0.557, P < 0.05) 3.2. Species richness and diversity

Species richness, species evenness and Shannon diversity differed significantly between NIG and IG (Supplementary Table 3), and were found lower in IG (Fig. 3) The Shannon diversity 11


assumed higher values in winter compared to rainy season (Fig. 3). In both NIG and IG treatments the number of forb species was higher compared to the number of graminoids in winter as well as in rainy seasons (Table 2). In NIG and IG both, number of forb species in winter season was 200% more than the number of graminoid species (Table 2). In the rainy season the number of forb species in NIG plots was 200% higher than the number of graminoid species, in the same season in the IG plots number of forbs was found to be 280% more than the number of graminoid species (Table 2). In the present study, 33 species belonging to 13 families were recorded (Supplementary Table 4), of which 4 were non-natives. Among these non-natives species, Ageratum conyzoides was present both in IG and NIG plots in winter as well as rainy seasons (Supplementary Table 5). Irrespective of the season, Oxalis corniculata and Tridax procumbens were present in IG, whereas Parthenium hysterophorus was only present in NIG (Supplementary Table 5). In winter season, 4 unique species occurred each in NIG and IG (Supplementary Tables 5, 6), while in rainy season, NIG and IG exibited 9 and 5 unique species, respectively (Supplementary Tables 5, 6). Common species between NIG and IG were 9 and 19 in winter and rainy season, respectively (Supplementary Table 6). Supplementary Table 5 summarizes the observed effect of Hyptis suaveolens invasion on the species composition of grassland community. H. suaveolens invasion suppressed three native graminoid species often present in the native grassland, such as Cyperus kyllingia, D. annulatum, E. tenella in winter season and two native forbs (namely, Malvastrum coromandelianum and Vernonia cinerea), and one non-native forb (P. hysterophorus). Occurrence of species was variable across the seasons.

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Results of principle component analysis using the IVI data for species in NIG and IG are summarized in Fig. 4. In winter season, the percent variation in species composition explained by axes 1 and 2 were 65 % and 8 %, respectively. In rainy season, however, the percentage of variance explained by the axes 1 and 2 were 39% and 17%, respectively. We found a significant correlation between IVI values of Hyptis with scores of axes 1 (R = 0.982; p = 0.01), which indicates the profound effect of Hyptis invasion on species composition. Further, the soil inorganic-N content and associated processes were found to be associated with species composition (Fig. 5). In winter season, certain species, (D. sanguinalis, O. corniculata, T. procumbens, Spilanthes acmela, Herpestris rugosa and R. pectinata) showed a preference toward higher values of soil nitrate, soil ammonium and related processes (nitrification, ammonification and N mineralization (Fig. 5), these species were abundant in IG. While certain other species showed preference towards higher values of soil moisture, soil temperature and MBC and these were concentrated in NIG plots (Fig. 5). 3.3. Soil properties and species diversity Diversity parameters were associated with soil moisture in rainy season, while soil temperature was positively associated with diversity parameters in winter season (Table 3). Species richness and Shannon diversity showed negative relationship with soil ammonium-N and nitrate-N, though more strongly with nitrate-N (Table 3). Similarly, N mineralization exhibited a negative relationship with species richness and Shannon diversity in both winter and rainy seasons, while evenness was negatively related with N-mineralization only in rainy season (Table 3). On the contrary, MBC showed a positive relationship with species richness and Shannon diversity in winter season and with all the diversity indices in rainy season (Table 3) 4. Discussion 13


Our study demonstrates a considerable effect of the introduction of H. suaveolens on soil properties and plant diversity in the dry tropical grassland. Other studies on invasion (Ehrenfeld 2003, Levine et al. 2003, Dassonville et al. 2008, Liao et al. 2008, Vilà et al. 2011) have also reported similar observations. We found lower soil temperature and moisture in IG (with lower plant diversity) than NIG (with higher plant diversity) plots. The observed lower soil temperature in IG than NIG in all seasons could be attributed to the reduction in the radiant energy in IG due to shade created by taller Hyptis cover. Pysek et al. (2012) reported that in 93.4% of cases, introduced plants are taller than 1.2 m, such as H. suaveolens, exerting a significant impact on the species composition. It has also been reported that a significant change in species composition alters environmental parameters such as albedo and transpiration rate (Dickinson 1983, Pielke 2001, Pitman 2003). Lower soil moisture in IG than NIG might be due to the faster resource utilization and high growth rate of Hyptis particularly during rainy season. Srivastava et al. (2016) have reported a shift in relative availability of N pools encountered with changing land use pattern. In this study, we also observed a considerable effect of vegetation on soil inorganic N content and associated microbial processes (N-mineralization). Tilman et al. (1996) found that soil mineral nitrogen was utilized more completely when there was a greater diversity of species. The experimental plantation of two invasives, Centaurea stoebe and Euphorbia esula caused enrichment of soil NO3-N just after one year of their establishment, suggesting the introduction of some invasive species can alter ecosystem functioning after a single year (McLeod et al. 2016). The IG plots, having lower species diversity than NIG, reflected a considerably higher amount of available soil N. The strong positive influence of Hyptis invasion on nitrate-N, ammonium-N, and nitrification, and negative effect on soil ammonium-N to nitrate-N ratio, MBC and pH in the present study suggests that these 14


variables could be associated with invasion mechanism. We argue that, Hyptis invasion significantly affects soil microbial community particularly the components that are associated with nitrification process. The lower MBC in IG compared to that in NIG could be a reflection of the deleterious effect of Hyptis invasion on soil microbial community through allelopathy. Kapoor (2011), Chatiyanon et al. (2012), Islam and Kato-Noguchi (2013) have demonstrated the presence of allelochemicals in the aqueous and methanol extracts of H suaveolens. A change in MBC may be associated with the change in the composition of microbial community and hence could result in altered rates of processes driven by the microbial community. Our study indicated higher soil nitrate-N content, ammonium-N content, and MBC in the summer season followed by winter and rainy seasons which is consistent with the trend reported for the dry tropics (Singh et al. 1989, Roy and Singh 1995). This evidently relates with the seasonality of nutrient demand and supply (Singh et al. 1989). The lowest rates of N mineralization were observed in summer and the highest in rainy season which can be attributed to the dependency of N mineralization on the availability of soil moisture. Being a microbial process, N mineralization is predominantly governed by soil moisture availability (Roy and Singh 1994). Lower diversity indices in IG than NIG in the present study indicate that Hyptis invasion had a significant depressive effect over plant diversity in the dry tropical grassland. We observed that the effect of invasion on plant diversity is mediated by the potential shift in soil nitrate-N availability, soil ammonium-N to nitrate-N ratio, nitrification rate and MBC. Further, the lower demand due to reduced diversity in IG, could result in higher availability of NO3-N and NH4-N in the soil. Tilman et al. (1996) reported that more species rich plots utilized more fully soil mineral-N than species poor plots. Moreover, studies have indicated a rapid (within one growing 15


season) effect of invasion on N-cycle (McLeod et al. 2016). The impact may substantially increase as Hyptis proliferates in the grassland with passage of time. In view of the results obtained in our short-term study, a long-term study is desirable. Shannon diversity in both IG and NIG showed higher values in winter than rainy season, suggesting that the impact of Hyptis invasion in winter season is relatively lower than in rainy season. Rainy season can be considered as the most favorable period for active growth due to optimum moisture and temperature conditions which are vigorously exploited by Hyptis to compete with and outgrow the native species. A positive relationship between soil moisture and soil ammonium-N to nitrate-N ratio and soil microbial biomass carbon can be argued to explain the effect of soil moisture on plant diversity in the rainy season. The lower number of unique species in IG than NIG as observed during rainy season, further indicated the preponderance of deleterious effect of Hyptis invasion on species diversity. 5. Conclusions In the dry tropical grassland, H. suaveolens showed a negative impact on plant diversity. The negative effect on plant diversity is mediated possibly by the effect of invasion on N mineralization processes (mainly nitrification), and consequently on the availability of soil inorganic-N pools. The study indicates that Hyptis invasion has an enormous potential to change the structure and composition of plant communities in the dry tropical grasslands. Acknowledgment TA gratefully acknowledges University Grant Commission (UGC, New Delhi) for providing Maulana Azad National Fellowship.

The authors are indebted to the coordinator, CAS,

Department of Botany, Banaras Hindu University for providing research facilities to carry out this research. PS also acknowledges the council of scientific and industrial research (CSIR, New 16


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Figure Legends:

Figure 1. Variations across seasons and treatments in (A) soil pH, (B) soil temperature, (C) soil moisture, (D) ammonium content, (E) nitrate content, (F) total inorganic nitrogen, (G) ammonium to nitrate ratio and (H) microbial biomass carbon in uninvaded grassland (NIG) and grassland invaded by H. suaveolens (IG). SE is shown as a thin linear bar.

Figure 2. Variations across seasons and treatments in (A) ammonification (B) nitrification and (C) N-mineralization rate in uninvaded grassland (NIG) and grassland invaded by H. suaveolens (IG). SE is shown as a thin linear bar. Figure 3. Effect of H. suaveolens on diversity indices of the grassland. SE is shown as a thin linear bar. Figure 4. Ordination showing the effect of H. suaveolens invasion on species composition of the grassland in two seasons by principal component analysis. (A) Winter season (B) Rainy season. Full names and authors of each species are given in Supplementary Table 2. Figure 5. Ordination showing the effect of soil selected properties and processes on species composition of the grassland in winter season by principal component analysis. Nit = nitrate-N content, Amm = ammonium-N content, Ammoni = ammonification, Nitri = nitrification, Min = N-mineralization, SM = soil moisture, ST = soil temperature, MBC = microbial biomass carbon. Full names and authors of each species are given in Supplementary Table 2.

25


TABLES

Table 1. Initial soil physio-chemical properties of the experimental plots

Soil properties

Value

Soil grain size analysis (%) Sand

4

Silt

85

Clay

11

Bulk density (g/m3)

1.24±0.01

Water Holding Capacity (%)

43.27±10.33

Total Organic Carbon (mg/g)

6.30±0.08

Total Nitrogen (mg/g)

0.64±0.06

C/N

10.08±0.86

Values are Mean ± 1SE.

26


Table 2. Number of species of different growth forms in NIG and IG plots during winter and rainy seasons Growth form

Uninvaded

Hyptis invaded

grassland

grassland

Winter

Rainy

Winter

Rainy

Number of forbs

8

21

9

19

Number of graminoids

6

7

3

5

27


Parameters Richness

Winter Evenness

Shannon diversity

Soil temperature

0.906**

0.301 NS

0.760*

Soil moisture

0.516NS

0.403 NS

NH4+-N

-0.947**

NO3--N N-mineralization MBC

Richness

Rainy Evenness

Shannon diversity

0.573 NS

0.454 NS

0.334 NS

0.441 NS

0.977**

0.884**

0.817**

-0.201 NS

-0.744*

-0.919**

-0.806**

-0.760*

-0.972**

-0.269 NS

-0.888**

-0.961**

-0.865**

-0.808**

-0.971**

-0.213 NS

-0.854**

-0.958**

-0.851**

-0.773**

0.922**

0.240 NS

0.698*

0.984**

0.906**

0.820**

Table 3. Pearson correlation coefficients between soil properties and diversity indices during winter and rainy seasons. The data were pooled across IG and NIG plots

* significance at P< 0.05, ** significance at P < 0.01, NS = Not significant

.

28


Figure 1 2.5

7.9

Uninvaded Grassland Hyptis invaded Grassland

A

Nitrate-N content ( g/g)

7.8

Uninvaded Grassland Hyptis invaded Grassland

E 2.0

Soil pH

7.7

7.6

1.5

7.5

7.4

1.0

7.3 0.5 7

7.2 50

F

40

Total inorganic-N ( g/g)

Soil temperature (ºC)

B

30

20

6

5

4

10 3 20

3.4

18

3.2

C

Ammonium to Nitrate ratio

Soil moisture (%)

16

G

3.0

14

2.8

12

2.6

10

2.4

2

2.2 2.0 1.8 1.6 500

Microbial biomass carbon ( g/g)

Ammonium-N content ( g/g)

0 5.0

D 4.5

4.0

3.5

29

3.0

450

H

400

350

300

250

200

150

2.5

Winter

Summer

Rainy

Winter

Summer

Rainy


10 Uninvaded Grassland Hyptis invaded Grassland

A Ammonification ( g/g/ month)

Figure 2 8

6

4

2

5.5

B

Nitrification ( g/ g/ month)

5.0

4.5

4.0

3.5

3.0

2.5

2.0 14

N-Mineralization ( g/ g/ month)

C 12

10

8

30

6

4 Downloaded from https://academic.oup.com/jpe/article-abstract/doi/10.1093/jpe/rtx045/4085044/Effect-of-invasion-by-Hyptis-suaveolens-on-plant by Banaras Hindu University user on 04 October 2017

Winter

Summer

Rainy

25

Winter season Rainy season

A

Species richness

20

15

10

5

Figure 3

0

4.5

B 4.0

Species evenness

3.5

3.0

2.5

2.0

1.5

1.0 2.2

C Shannon diversity (H')

2.0

1.8

1.6

1.4

31 1.2

1.0 Downloaded from https://academic.oup.com/jpe/article-abstract/doi/10.1093/jpe/rtx045/4085044/Effect-of-invasion-by-Hyptis-suaveolens-on-plant by Banaras Hindu University user on 04 October 2017

Uninvaded Grassland

Hyptis Invaded

Axis 2

Figure 4

Des ga

A

Sco du Era br Cyno da Ver ci

Dic an

Cyp tu Era pi Par hy

Dig sa Axis 1

Cyp ro Sid ac

Run pe

Mal sp

Tri pr Oxa co Spi ac

Age co

Axis 2

Her ru

B

Hyptis

Sco du Ipo pa Era te

Mal sp Aty ma Cyp ky Old co Opl co Abu in Par hy Dig sa Ani ov Her ru

Cyno da Spi ac

Tin co

Van cr

Cyp ro Ure re

Age co Axis 1

Run pe

Bar cr

Hyptis

Phy si Des ga Oxa co

Cor ca Cli te Tri pr

Com be

Sid ac Phy ni Dic an

32


Nit

Min

Amm Nitri

Ammoni

Her ru Spi ac

Axis 2

Figure 5

Oxa co Age co Tri pr Run pe Mal sp

Sid ac

Cyp ro Dig sa

Sco du

Axis 1

SM

Par hy Cyno da

Era pi

Cyp tu Ver ci Dic an

Era br MBC

ST

Des ga

33
