Data are the pooled means of three estimates each over two years **±** standard deviation. 'p-value' denotes the significance of difference between the means by one way ANOVA statistics. a The values

**\* Cul**: *Cassia uniflora* Mill.non Spreng ; **Snl**: *Synedrella nodiflora*(L) Gaertn; **Alt**: *Alternanthera tenella* Colla; **Eug**: *Euphorbia geniculata* Orteg.; **Ach**: *Achyranthes aspera* L.; **Bod**: *Boerhaavia erecta* L.; **Bln**: *Blainvillea acmella* L.; **Aca**: *Acalypha ciliata* Forsk.; **Tum:** *Triumfetta rhomboidea* Jacq.; **Cab**: *Cassia absus* L.; **Cfl:** *Cassia obtusifolia* L.; **Bdn**: *Bidens biternata* Lour.; **Raw:** *Rauwolfia tetraphylla* L.; **Opl:** *Oplismenus compositus* P.Beauv.

followed by different letters differ significantly by Duncan's multiple range test at p=0.05.

Table 4. Photosynthetic parameters of invasive and native weeds

<0.001 <0.001 <0.001 <0.001 0.81 <0.001 <0.001

Transp. rate mmol cm-2 sec-1

> 1.181 a ± 0.21

1.152 ab ± 0.242

1.053 abc ± 0.13

1.048 bcd ± 0.033

1.052 abc ± 0.095

0.874 cde ± 0.16

0.968 cd ± 0.28

0.73 0.845 cde ± 0.020 25.84

0.889 cde ± 0.19

0.94 0.731 def ± 0.038 26.68

1.35 0.832 cde ± 0.032 25.88

1.016 bcd ± 0.15

0.702 ef ± 0.0603

0.592 f ± 0.047

WUE μmolm mol-1

> 25.02 ± 1.00

> 25.28 ± 1.26

> 25.93 ± 1.81

> 25.89 ± 0.78

> 25.88 ± 1.55

> 25.29 ± 1.52

> 24.08 ± 0.96

> ± 1.81

25.29 ± 0.76

± 1.33

± 0.78

26.12 ± 1.57

25.45 ± 1.78

25.82 ± 1.03 DMAR / m2/ day

19.16 a ± 0.77

> 5.90b ± 0.30

> 4.18c ± 0.29

> 2.66d ± 0.08

> 2.58d ± 0.15

> 2.62d ± 0.16

0.46gh ± 0.02

0.85fg ± 0.06

> 1.46e ± 0.04

> 0.26h ± 0.01

0.58gh ± 0.02

1.09ef ± 0.07

> 0.32h ± 0.02

> 0.16h ± 0.01

Dry weight / plant g

12.40 b ± 0.50

4.10g ± 0.21

8.30f ± 0.58

4.60g ± 0.14

10.20d ± 0.61

10.70cd ± 0.64

1.43jk ± 0.06

> 1.75ij ± 0.12

11.35c ± 0.34

> 3.02h ± 0.15

17.43a ± 0.52

2.35hi ± 0.14

> 9.50e ± 0.66

> 0.98k ± 0.04

over three native grasses.

Snl 29.122 ab ±

Eug 27.137 ab ±

Ach 27.237 ab ±

Bln 23.308 bc ±

Aca 21.833 bc ±

Photosynthetic rate µmol cm-2 sec-1

Stomatal conductance mmol cm-2 sec-1

6.15 0.351ab ± 0.038 14.90e ±

3.06 0.318a ± 0.027 18.41d ±

2.01 0.324a ± 0.027 12.20fg

8.59 0.272bc ± 0.10 13.00ef

0.45 0.253bcd ± 0.006 10.50g ±

Cul 29.55 a ± 4.84 0.353a ± 0.064 20.41 d

Alt 27.3ab ± 0.43 0.34a ± 0.072 12.80ef

Bod 22.1 bc ± 3.79 0.256bc ± 0.041 11.80fg

Tum 22.483bc ± 5.01 0.266bc ± 0.058 33.66c ±

Cab 19.5c ± 0.7 0.178de ± 0.014 18.83d ±

Cfl 21.533bc ± 0.51 0.21cde ± 0.018 45.00a ±

Bdn 26.542ab ± 3.88 0.309a ± 0.044 33.10c ±

Raw 17.867c ± 1.53 0.143e ± 0.033 42.66b ±

Opl 15.283d ± 1.38 0.125e ± 0.015 3.50h ±

DMAR – Dry Matter Accumulation Rate

Weed Sps.

accumulation of reserved food materials like starch and dry matter accumulation rate and dry biomass. Considering this the dominance of *Cassia, Synedrella* and other native weeds can be correlated with higher amount of chlorophyll contents, enhanced photosynthetic rate and increased accumulation of reserved food materials.

### **4.7 Carbon assimilation rate of invasive and native weeds**

The selected invasive weeds like *Cassia, Synedrella* and *Alternanthera* had shown the highest photosynthetic rate, stomatal conductance and transpiration rate as compared to native weeds such as *Achyranthes* and *Boerhaavia* (Table 4). Amongst the natives *Achyranthes* was superior in all above mentioned parameters over other weeds like *Triumfetta, Boerhaavia, Cassia absus* and *Rauwolfia*.

The third leaf area was maximum in *Cassia obtusifolia*, which was followed by *Rauwolfia* and *Triumfetta*. There was no significant difference in water use efficiency (WUE) amongst the investigated invasive and native weeds. On the basis of dry matter accumulation rate (DMAR) *Cassia uniflora* was topmost, which was followed by *Synedrella* and *Alternanthera.*  Similarly the results for dry weight per plant (Table 4) indicated highest values for *Cassia obtusifolia* followed by *Cassia uniflora* and *Boerhaavia.* 

According to McDowell (2002) the success of invasion and dominance of invasive weeds in any ecosystem over co-occurring species can be ascribed to their superiority in physiological attributes like photosynthetic rate, stomatal conductance, third leaf area and DMAR, but all such parameters mostly remained unexplained and unexplored. Understanding of such factors may give valuable insight to resolve the problem of invasion. Photosynthesis is the key catabolic process in the life cycle of any plant, which synthesizes various types of photoassimilates and reflects into overall productivity and metabolic status of that plant. The secondary metabolites acting as allelochemicals are mainly derived from carbohydrates synthesis during photosynthesis.

Research workers like Durand and Goldstein (2001) and Ewe and Sternberg (2003) have also recorded the significant difference in photosynthetic rate, stomatal conductance, transpiration rate and total leaf area for the various invasive weeds and claimed that these weeds were highly dominant over the associated natives because of their superiority in above parameters.

According to Pattison et al. (1998) successful invasive species should have elite morphological and physiological traits, which increase their photon capturing ability and light utilization efficiency. But unfortunately this type of invagination has remained obscure due to paucity of experimental work, except few reports on light capturing mechanism, photon-saturated photosynthetic rate, specific leaf area (SLA) investigated in some invasive weeds by Ewe and Sternberg (2003). According to Durand and Goldstein (2001) invasiveness of alien species is dependent on photosynthetic efficiency. They further claimed that invasive species have a higher ability to capture solar radiations at the minimum cost of energy (ATP), diverting more resources for their growth, development, reproduction and yield. Coupled with the above distinctive features of photosynthesis, the invasive weeds have very high abiotic stress tolerance capacity, which enables them to survive and reproduce successfully, under extremely harsh environmental conditions like drought.

The water use efficiency (WUE) is always positively co-related with the rate of photosynthesis, however in present studies it has not shown any significant differences,

accumulation of reserved food materials like starch and dry matter accumulation rate and dry biomass. Considering this the dominance of *Cassia, Synedrella* and other native weeds can be correlated with higher amount of chlorophyll contents, enhanced photosynthetic rate

The selected invasive weeds like *Cassia, Synedrella* and *Alternanthera* had shown the highest photosynthetic rate, stomatal conductance and transpiration rate as compared to native weeds such as *Achyranthes* and *Boerhaavia* (Table 4). Amongst the natives *Achyranthes* was superior in all above mentioned parameters over other weeds like *Triumfetta, Boerhaavia,* 

The third leaf area was maximum in *Cassia obtusifolia*, which was followed by *Rauwolfia* and *Triumfetta*. There was no significant difference in water use efficiency (WUE) amongst the investigated invasive and native weeds. On the basis of dry matter accumulation rate (DMAR) *Cassia uniflora* was topmost, which was followed by *Synedrella* and *Alternanthera.*  Similarly the results for dry weight per plant (Table 4) indicated highest values for *Cassia* 

According to McDowell (2002) the success of invasion and dominance of invasive weeds in any ecosystem over co-occurring species can be ascribed to their superiority in physiological attributes like photosynthetic rate, stomatal conductance, third leaf area and DMAR, but all such parameters mostly remained unexplained and unexplored. Understanding of such factors may give valuable insight to resolve the problem of invasion. Photosynthesis is the key catabolic process in the life cycle of any plant, which synthesizes various types of photoassimilates and reflects into overall productivity and metabolic status of that plant. The secondary metabolites acting as allelochemicals are mainly derived from carbohydrates

Research workers like Durand and Goldstein (2001) and Ewe and Sternberg (2003) have also recorded the significant difference in photosynthetic rate, stomatal conductance, transpiration rate and total leaf area for the various invasive weeds and claimed that these weeds were highly dominant over the associated natives because of their superiority in

According to Pattison et al. (1998) successful invasive species should have elite morphological and physiological traits, which increase their photon capturing ability and light utilization efficiency. But unfortunately this type of invagination has remained obscure due to paucity of experimental work, except few reports on light capturing mechanism, photon-saturated photosynthetic rate, specific leaf area (SLA) investigated in some invasive weeds by Ewe and Sternberg (2003). According to Durand and Goldstein (2001) invasiveness of alien species is dependent on photosynthetic efficiency. They further claimed that invasive species have a higher ability to capture solar radiations at the minimum cost of energy (ATP), diverting more resources for their growth, development, reproduction and yield. Coupled with the above distinctive features of photosynthesis, the invasive weeds have very high abiotic stress tolerance capacity, which enables them to survive and reproduce successfully, under extremely harsh environmental conditions like

The water use efficiency (WUE) is always positively co-related with the rate of photosynthesis, however in present studies it has not shown any significant differences,

and increased accumulation of reserved food materials.

*obtusifolia* followed by *Cassia uniflora* and *Boerhaavia.* 

*Cassia absus* and *Rauwolfia*.

synthesis during photosynthesis.

above parameters.

drought.

**4.7 Carbon assimilation rate of invasive and native weeds** 

amongst the invasive and native weed species investigated. Funk and Vitousek (2007) have reported the positive co-relation with leaf traits and WUE in some weeds. Blicker et al. (2003) had also reported higher water use efficiency in the invasive weed *Centaurea maculosa* over three native grasses.


DMAR – Dry Matter Accumulation Rate
