Stem density and size stratification of woody species are informative of vegetation conditions and its physiognomy in savannah whereas their variation influence woody population functioning. Current study endeavoured ...Stem density and size stratification of woody species are informative of vegetation conditions and its physiognomy in savannah whereas their variation influence woody population functioning. Current study endeavoured to evaluate the stand density and size variability of woody species related to aboveground biomass in a Sudanian savannah. Total height, stem diameter at breast height (dbh) ≥ 5 cm were measured in 30 plots of 50 m </span></span><span><span><span style="font-family:"">×<span> 20 m laid in respect to vegetation type as bowal, shrubland and woodland. Species diversity, stem density, height and basal area were calculated and compared across sites and variation in stem dbh classes evaluated. Total aboveground biomass was estimated and thereafter linear relationships were established between stand density and aboveground biomass</span></span></span></span><span><span><span style="font-family:"">,</span></span></span><span><span><span style="font-family:""> and basal area. Results revealed three different sites with an overall 58 species identified through vegetation type including liana species (4 stems in bowal) with 18 genera and 42 families. Fabaceae Combretaceae, Anacardiaceae and Rubiaceae were dominant families. Small sized trees represented 72% of total stem density considered in structure with significant higher basal area, while large sized trees as 28% were scarcely distributed. More than 70% variation in biomass w</span></span></span><span><span><span style="font-family:"">as </span></span></span><span><span><span style="font-family:"">due to stem density and basal area with a dominance of small trees. In conclusion increase size in tree community indicated increase in accumulated aboveground biomass as positive regeneration features. But, change in vegetation structure strongly influence negatively species ability to grow from lower to upper size class and later on, disrupt ecosystem functioning. Plant stem density and stratification could be considered as indicators of aboveground biomass fluctuating in regeneration monitoring.展开更多
The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances...The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances. To explore the mechanisms underlying the effect of spring fire and topography on the aboveground biomass(AGB) and the soil C and N pool, we conducted a field experiment between April 2014 and August 2016 in a semi-arid grassland of northern China to examine the effects of slope and spring fire, and their potential interactions on the AGB and organic C and total N contents in different plant functional groups(C_3 grasses, C_4 grasses, forbs, Artemisia frigida plants, total grasses and total plants).The dynamics of AGB and the contents of organic C and N in the plants were examined in the burned and unburned plots on different slope positions(upper and lower). There were differences in the total AGB of all plants between the two slope positions. The AGB of grasses was higher on the lower slope than on the upper slope in July. On the lower slope, spring fire marginally or significantly increased the AGB of C_3 grasses, forbs, total grasses and total plants in June and August, but decreased the AGB of C_4 grasses and A.frigida plants from June to August. On the upper slope, however, spring fire significantly increased the AGB of forbs in June, the AGB of C_3 grasses and total grasses in July, and the AGB of forbs and C_4 grasses in August. Spring fire exhibited no significant effect on the total AGB of all plants on the lower and upper slopes in 2014 and 2015. In 2016, the total AGB in the burned plots showed a decreasing trend after fire burning compared with the unburned plots. The different plant functional groups had different responses to slope positions in terms of organic C and N contents in the plants. The lower and upper slopes differed with respect to the organic C and N contents of C_3 grasses, C_4 grasses, total grasses, forbs, A. frigida plants and total plants in different growing months. Slope position and spring fire significantly interacted to affect the AGB and organic C and N contents of C_4 grasses and A. frigida plants. We observed the AGB and organic C and N contents in the plants in a temporal synchronized pattern. Spring fire affected the functional AGB on different slope positions, likely by altering the organic C and N contents and, therefore,it is an important process for C and N cycling in the semi-arid natural grasslands. The findings of this study would facilitate the simulation of ecosystem C and N cycling in the semi-arid grasslands in northern China.展开更多
Nutrient addition can affect the structure and diversity of grassland plant communities, thus alter the grassland productivity. Studies on grassland plant community composition, structure and diversity in response to ...Nutrient addition can affect the structure and diversity of grassland plant communities, thus alter the grassland productivity. Studies on grassland plant community composition, structure and diversity in response to nutrient addition have an important theoretical and practical significance for the scientific management of grassland, protection of plant diversity and the recovery of degraded grassland. A randomized block design experiment was conducted with six blocks of eight treatments each： control（no nutrient addition） and K, P, N, PK, NK, NP, and NPK addition. We evaluated plant composition, height, coverage, density, and aboveground biomass to estimate primary productivity and plant diversity. Results showed that all treatments increased primary productivity significantly（P〈0.05） with the exception of the K and the NPK treatments had the greatest effect, increasing aboveground biomass 2.46 times compared with the control（P〈0.05）. One-way ANOVA and factorial analysis were used for the species richness, Shannon-Wiener index, Pielou index and aboveground biomass, and the relationships between the diversity indices and aboveground biomass were determined through linear regression. We found that fertilization altered the community structure; N（but not P or K） addition increased the proportion of perennial rhizome grasses and significantly reduced that of perennial forbs（P〈0.05）, thus it presented a trend of decrease in species richness, Shannon-Wiener and Pielou indexex, respectively. Only the main effects of N had significant impacts on both the diversity indices and the aboveground biomass（P〈0.05）, and the interactions between N-P, N-K, P-K and N-P-K could be neglected. With fertilization, plant diversity（correlation coefficient, –0.61）, species richness（–0.49）, and species evenness（–0.51） were all negatively linearly correlated with primary productivity. The correlations were all significant（P〈0.01）. Scientific nutrient management is an effective way to improve grassland productivity, protect the plant diversity as well as recover the degraded grassland.展开更多
文摘Stem density and size stratification of woody species are informative of vegetation conditions and its physiognomy in savannah whereas their variation influence woody population functioning. Current study endeavoured to evaluate the stand density and size variability of woody species related to aboveground biomass in a Sudanian savannah. Total height, stem diameter at breast height (dbh) ≥ 5 cm were measured in 30 plots of 50 m </span></span><span><span><span style="font-family:"">×<span> 20 m laid in respect to vegetation type as bowal, shrubland and woodland. Species diversity, stem density, height and basal area were calculated and compared across sites and variation in stem dbh classes evaluated. Total aboveground biomass was estimated and thereafter linear relationships were established between stand density and aboveground biomass</span></span></span></span><span><span><span style="font-family:"">,</span></span></span><span><span><span style="font-family:""> and basal area. Results revealed three different sites with an overall 58 species identified through vegetation type including liana species (4 stems in bowal) with 18 genera and 42 families. Fabaceae Combretaceae, Anacardiaceae and Rubiaceae were dominant families. Small sized trees represented 72% of total stem density considered in structure with significant higher basal area, while large sized trees as 28% were scarcely distributed. More than 70% variation in biomass w</span></span></span><span><span><span style="font-family:"">as </span></span></span><span><span><span style="font-family:"">due to stem density and basal area with a dominance of small trees. In conclusion increase size in tree community indicated increase in accumulated aboveground biomass as positive regeneration features. But, change in vegetation structure strongly influence negatively species ability to grow from lower to upper size class and later on, disrupt ecosystem functioning. Plant stem density and stratification could be considered as indicators of aboveground biomass fluctuating in regeneration monitoring.
基金supported by the National Key Basic Research and Development Program of China (2016YFC0500703)the National Natural Science Foundation of China (31572452, 41573063, 31870438)
文摘The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances. To explore the mechanisms underlying the effect of spring fire and topography on the aboveground biomass(AGB) and the soil C and N pool, we conducted a field experiment between April 2014 and August 2016 in a semi-arid grassland of northern China to examine the effects of slope and spring fire, and their potential interactions on the AGB and organic C and total N contents in different plant functional groups(C_3 grasses, C_4 grasses, forbs, Artemisia frigida plants, total grasses and total plants).The dynamics of AGB and the contents of organic C and N in the plants were examined in the burned and unburned plots on different slope positions(upper and lower). There were differences in the total AGB of all plants between the two slope positions. The AGB of grasses was higher on the lower slope than on the upper slope in July. On the lower slope, spring fire marginally or significantly increased the AGB of C_3 grasses, forbs, total grasses and total plants in June and August, but decreased the AGB of C_4 grasses and A.frigida plants from June to August. On the upper slope, however, spring fire significantly increased the AGB of forbs in June, the AGB of C_3 grasses and total grasses in July, and the AGB of forbs and C_4 grasses in August. Spring fire exhibited no significant effect on the total AGB of all plants on the lower and upper slopes in 2014 and 2015. In 2016, the total AGB in the burned plots showed a decreasing trend after fire burning compared with the unburned plots. The different plant functional groups had different responses to slope positions in terms of organic C and N contents in the plants. The lower and upper slopes differed with respect to the organic C and N contents of C_3 grasses, C_4 grasses, total grasses, forbs, A. frigida plants and total plants in different growing months. Slope position and spring fire significantly interacted to affect the AGB and organic C and N contents of C_4 grasses and A. frigida plants. We observed the AGB and organic C and N contents in the plants in a temporal synchronized pattern. Spring fire affected the functional AGB on different slope positions, likely by altering the organic C and N contents and, therefore,it is an important process for C and N cycling in the semi-arid natural grasslands. The findings of this study would facilitate the simulation of ecosystem C and N cycling in the semi-arid grasslands in northern China.
基金project was supported by the National Natural Science Foundation of China (31170435)the Key Technologies R&D Program of China during the 12th Five-Year Plan period (2012BAD13B07)+1 种基金the Fundamental Research Laboratory of the Central-Level Nonprofit Research Institutes, Chinathe Open Fund of the Key Laboratory of Environmental Quality in the Ministry of Agriculture and Agricultural Environment and Safety of Agricultural Products in Tianjin, China
文摘Nutrient addition can affect the structure and diversity of grassland plant communities, thus alter the grassland productivity. Studies on grassland plant community composition, structure and diversity in response to nutrient addition have an important theoretical and practical significance for the scientific management of grassland, protection of plant diversity and the recovery of degraded grassland. A randomized block design experiment was conducted with six blocks of eight treatments each： control（no nutrient addition） and K, P, N, PK, NK, NP, and NPK addition. We evaluated plant composition, height, coverage, density, and aboveground biomass to estimate primary productivity and plant diversity. Results showed that all treatments increased primary productivity significantly（P〈0.05） with the exception of the K and the NPK treatments had the greatest effect, increasing aboveground biomass 2.46 times compared with the control（P〈0.05）. One-way ANOVA and factorial analysis were used for the species richness, Shannon-Wiener index, Pielou index and aboveground biomass, and the relationships between the diversity indices and aboveground biomass were determined through linear regression. We found that fertilization altered the community structure; N（but not P or K） addition increased the proportion of perennial rhizome grasses and significantly reduced that of perennial forbs（P〈0.05）, thus it presented a trend of decrease in species richness, Shannon-Wiener and Pielou indexex, respectively. Only the main effects of N had significant impacts on both the diversity indices and the aboveground biomass（P〈0.05）, and the interactions between N-P, N-K, P-K and N-P-K could be neglected. With fertilization, plant diversity（correlation coefficient, –0.61）, species richness（–0.49）, and species evenness（–0.51） were all negatively linearly correlated with primary productivity. The correlations were all significant（P〈0.01）. Scientific nutrient management is an effective way to improve grassland productivity, protect the plant diversity as well as recover the degraded grassland.
