Leaf Construction Cost and Related Ecophysiological Parameters of Rice Crop and Its Important Weeds

To understand the reason for the success of weeds,we investigated the energetic cost of leaf construction,and certain ecophysiological traits of rice and its dominant weeds.On physiological basis among all weeds,Caesulia axillaris Roxburgh was found to be the most serious,followed by Echinochloa cruss-galli L.Beauv and Echinochloa colonum L.Link,while Fimbristylis miliaceae L.Vahl and Cyperus iria L.were moderate weeds of the rice fields.C.axillaris had the lowest leaf construction cost （LCC） both on a mass basis （1.15 g/g） and on a unit area basis （22.93 g/m2）.Comparatively higher specific leaf area,photosynthetic rate,photosynthetic nitrogen use efficiency,leaf area ratio and leaf area index provided C.axillaris with further competitive advantage.Low LCC suggests that weeds utilize carbon resource more efficiently than the crop and potentially spend the saved energy on other competitive strategies viz.seed production,biomass production and high relative growth rate,which results in low crop yield and increase in weed seed bank.

Soil Carbon Dynamics Under Changing Climate A Research Transition from Absolute to Relative Roles of Inorganic Nitrogen Pools and Associated Microbial Processes:A Review

It is globally accepted that soil carbon （C） dynamics are at the core of interlinked environmental problems, deteriorating soil quality and changing climate. Its management remains a complex enigma for the scientific community due to its intricate relationship with soil nitrogen （N） availability and moisture-temperature interactions. This article reviews the management aspects of soil C dynamics in light of recent advances, particularly in relation to the availability of inorganic N pools and associated microbial processes under changing climate. Globally, drastic alterations in soil C dynamics under changing land use and management practices have been primarily attributed to the variation in soil N availability, resulting in a higher decomposition rate and a considerable decline in soil organic C （SOC） levels due to increased soil CO2 emissions, degraded soil quality, and increased atmospheric CO2 concentrations, leading to climate warming. Predicted climate warming is proposed to enhance SOC decomposition, which may further increase soil N availability, leading to higher soil CO2 effiux. However, a literature survey revealed that soil may also act as a potential C sink, if we could manage soil inorganic N pools and link microbial processes properly. Studies also indicated that the relative, rather than the absolute, availability of inorganic N pools might be of key importance under changing climate, as these N pools are variably affected by moisture-temperature interactions, and they have variable impacts on SOC turnover. Therefore, multi-factorial studies are required to understand how the relative availability of inorganic N pools and associated microbial processes may determine SOC dynamics for improved soil C management.

Effects of light availability on leaf attributes and seedling growth of four tree species in tropical dry forest

Background:In tropical dry forests,variation in understory light availability due to season and canopy tree density could be a governing factor in establishment and growth of tree seedlings.Species with varying life history traits are expected to respond differentially to such heterogeneity.We investigated the response of seedlings of four tree species in a tropical day forest in relation to spatiotemporal variability of light.We attempt to explore the role of leaf attributes in explaining intra-and inter-specific variations in relative growth rate.Four study sites,each with three contrasting canopy conditions,were selected along a soil moisture gradient.Seedlings of four tree species(viz.,Acacia catechu,Bridelia retusa,Lagerstroemia parviflora,and Shorea robusta),varying in life history traits,were monitored for seasonal variations in growth traits across canopy condition and sites for 2 years.Results:We observed a larger variation in leaf attributes for pioneer species.A.catechu showed highest mean values for leaf dry matter content,leaf nitrogen concentration,leaf phosphorus concentration,net stomatal conductance,net photosynthetic rate,and relative growth rate in high light conditions.S.robusta and B.retusa demonstrated highest mean values for all the leaf attributes(except leaf dry matter content)in low light conditions.However,intermediate values for leaf attributes were observed in L.parviflora which preferred moderate light conditions.Conclusions:Seasonal variations in light availability at the forest floor appear to play an important role in the establishment and growth of tree seedlings in seasonal dry forests.Leaf attributes can be used to explain intra-and inter-specific variation in response to light availability.Leaf attributes in combinations can be used to predict relative growth rate of tree species in tropical dry environment,which apart from soil moisture is also determined by light availability due to seasonal changes and canopy tree density.

Comparative response of seedlings of selected native dry tropical and alien invasive species to CO_(2) enrichment

Global climate change and ongoing plant invasion are the two prominent ecological issues threatening biodiversity world wide.Among invasive species,Lantana camara and Hyptis suaveolens are the two most important invaders in the dry deciduous forest in India.We monitored the growth of these two invasive species and seedlings of four native dry deciduous species(Acacia catechu,Bauhinia variegata,Dalbergia latifolia and Tectona grandis)under ambient(375–395μmol mol^(-1))and elevated CO_(2)(700–750μmol mol^(-1))to study the differential growth response of invasive and native seedlings.Methods Seedlings of all the species were exposed to ambient and elevated CO_(2).After 60 days of exposure,seedlings were harvested and all the growth-related parameters like plant height;biomass of root,stem and leaves;total seedling biomass;R/S ratio;allocation parameters;net assimilation rate(NAR)and relative growth rate(RGR)were determined.Important Findings Biomass,RGR and NAR of all the species increased under elevated CO_(2)but the increase was higher in invasive species and they formed larger seedlings than natives.Therefore under the CO_(2)-enriched future atmosphere,competitive hierarchies could change and may interfere with the species composition of the invaded area.

comSeedling growth of five tropical dry forest tree species in relation to light and nitrogen gradients

Aims Increasing anthropogenic nitrogen(N)deposition has been claimed to induce changes in species composition and community dynamics.A greenhouse experiment was conducted to examine the effect of increased N availability on growth and functional attributes of seedlings of five tree species with different life history characteristics under varying irradiances.The following questions have been addressed:(i)how do the pioneer and non-pioneer species respond in absolute growth and relative growth rate(RGR)to the interaction of light and nitrogen?(ii)how does the interaction between irradiance and nitrogen availability modulate growth attributes(i.e.functional attributes)?(iii)is there any variation in growth responses between leguminous and non-leguminous species along the light and nitrogen gradients?Methods Seedlings of five tree species(Acacia catechu,Bridelia retusa,Dalbergia sissoo,Lagerstroemia parviflora and Terminalia arjuna)were subjected to twelve combinations of irradiance and N levels.Various growth traits,including height(HT),basal area(BA),whole plant dry biomass(MD),leaf mass per unit area(LMA),leaf area ratio(LAR),net assimilation rate(NAR),RGR,biomass fractions,root-toshoot ratio(R:S)and leaf nitrogen content,were studied to analyse intra-and inter-specific responses to interacting light and N gradients.Important Findings Significant interactions for irradiance and N availability for majority of growth attributes indicates that growth and biomass allocation of seedlings were more responsive to N availability under high irradiance.However,species responded differentially to N addition and they did not follow successional status.Slow growers(B.retusa,a shade-tolerant species and L.parviflora,a light demander)exhibited greater response to N enrichment than the fast growers(A.catechu,D.sissoo and T.arjuna).However,N-mediated increment in growth traits was greater in non-legumes(B.retusa,L.parviflora and T.arjuna)compared with that of legumes(A.catechu and D.sissoo).Allocation of biomass to root was strongly suppressed at the highest N supply across species;however,at high irradiance and high N availability,a greater suppression in R:S ratio was observed for B.retusa.NAR was a stronger determinant of RGR relative to LAR,suggesting its prominent role in increased RGR along increasing irradiances.Overall,a higher growth response of slow-growing species to elevated N levels,particularly the non-pioneers(B.retusa and L.parviflora)suggests that future N deposition may lead to perturbations in competition hierarchies and species composition,ultimately affecting community dynamics in nutrient-poor tropical dry forests.

Relative effects of different leaf attributes on sapling growth in tropical dry forest

Aims Soil moisture content(SMC)influences establishment,survival and development of plant species and is considered as the most important limiting factor in tropical dry forest(TDF).In this study we attempt to establish the relationship between leaf attributes and of tree saplings in TDF and address the following questions:(i)how are the functional attributes of dominant tree saplings of TDF affected by seasonal changes in SMC at different habitats?,(ii)what is the relationship of functional attributes with each other?,(iii)how are the functional attributes and their plasticity affected by habitat con-ditions?and(iv)can the functional attributes in single or in com-bination predict the growth rate of tree saplings of TDF?The study was conducted on four sites(Hathinala,Gaighat,Harnakachar and Ranitali,listed in order of decreasing SMC)within the tropical dry deciduous forest in northern India.Methods We analysed eight leaf attributes,specific leaf area(SLA);leaf dry matter content(LDMC);leaf nitrogen concentration(leaf N);leaf phosphorus concentration(leaf P);chlorophyll concentration(Chl);mass-based photosynthetic rate(Amass);mass-based stomatal con-ductance(Gsmass);intrinsic water use efficiency(WUEi)and three growth attributes,relative diameter increment(RDI);relative height increment(RHI);relative growth rate(RGR)of the 10 dominant tree saplings(viz.,Acacia catechu,Anogeissus latifolia,Boswellia serrata,Buchanania lanzan,Diospyros melanoxylon,Hardwickia binata,Lagerstroemia parviflora,Lannea coromandelica,Shorea robusta and Terminalia tomentosa)of a TDF and observed the effects of site,season and species for a period of 2 years.Saplings were selected in gradients of deciduousness.Step-wise multiple regression was performed to predict RDI,RHI and RGR from mean values of SMC and leaf attributes.Important Findings All the 11 attributes were interrelated and differed significantly among the 10 saplings.Species response varied across sites and seasons.Across the SMC gradient,the attributes showed variable plasticity that differed across species.Among the 10 saplings,the highly deciduous Boswellia serrata showed the maximum plasticity in seven functional attributes.According to the step-wise multiple regressions,65%variability in RDI and 67%variability in RGR were due to Gsmass,and for RHI,61%variability was due to Amass.SMC and the other attributes,viz.,SLA,Chl,WUEi and LDMC in combination could contribute only for~2-6%of the variability in RDI,RHI and RGR,which indicates that other traits/factors,not accounted in this study are also important in modulating the growth of tree saplings in TDFs.In conclusion,growth of the tree saplings in the tropical dry environment is determined by soil moisture,whereas the response of saplings of different tree species is modulated by alterations in key functional attributes such as SLA,Chl,WUEi and LDMC.

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

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 inves-tigated that how does the H.suaveolens invasion regulate plant spe-cies 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,2×2m)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 indi-viduals of H.suaveolens were transplanted per plot.After 1 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 mois-ture content and temperature than NIG in rainy season,whereas soil ammonium-N,nitrate-N,total inorganic-N,N mineralization registered higher values for IG than NIG in both rainy and win-ter 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 significantly correlated with the ratio of ammonium-N to nitrate-N.The negative effect of invasion by H.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 poten-tial to change the structure and composition of plant communities in the dry tropical grasslands.