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Spatial heterogeneity of soil seed banks in sandy grasslands under fencing and grazing in Horqin sandland, Northern China

Zuo X., Zhao X., Zhao H., Zhang T., Wang S., Knops J., Kochsiek A.

Polish Journal of Ecology

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2013

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Vol. 61, nr 2

221--231

EN

Understanding composition, structure and spatial heterogeneity in soil seed banks is important for the management of grassland ecosystem. Although the effect of fencing and grazing on vegetation composition is widely known, information on species composition, seed density and spatial heterogeneity of soil seed banks in sandy grasslands under fencing and grazing is still lacking. We measured the species composition and seed density of soil seed banks in fenced grassland, grazed grassland and grazed shrubby grassland in Horqin Sand Land, Northern China. By applying the geostatistical methods, we assessed how fencing and grazing affected spatial heterogeneity of soil seed banks in sandy grasslands. Total seed density and species richness in soil seed banks were lower in fenced grassland than in either grazed grassland or grazed shrubby grassland. Seed density and species richness of annual species in soil seed banks were also lower in fenced grassland than in either grazed grassland or grazed shrubby grassland, while those of perennial species showed a reverse trend. The analysis of spatial autocorrelation ranges, fractal dimensions and distribution pattern maps from geostatistical methods showed that spatial heterogeneity of seed density and species richness in soil seed banks were also lower in fenced grassland than in either grazed grassland or grazed shrubby grassland. Continuous fencing increases the seed density and species richness of perennial species in soil seed banks, as well as results in a decrease in spatial heterogeneity of seed density and species richness in soil seed banks. So, continuous fencing should be considered to restore the degraded sandy grasslands in management of semiarid grassland ecosystems.

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Variations in foliar nutrient resorption efficiency of different plant growth forms in a temperate sandy grassland

Mao W., Li Y., Cui J., Zuo X., Zhao X.

Polish Journal of Ecology

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2011

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Vol. 59, nr 2

355-365

EN

Foliar nutrient resorption is an important strategy which allows leaf nutrients to be reused rather than lost with leaf fall, particularly in nutrient-poor ecosystems where even small nutrient losses can have significantly negative impacts on plant survival, competitive ability, and fitness. However, plants vary greatly in nitrogen (N) and phosphorus (P) resorption among plant growth forms during leaf senescence, which may be vital to understand the role of plant growth forms in ecosystem functioning. Green and senesced leaf N and P concentrations of 39 plant species in sandy grassland (Horqin Sand Land) of northern China were analyzed to detect variations of nutrient resorption efficiency among plant growth forms. The results showed that nitrogen resorption efficiency (NRE) ranged from 29% to 74%, with an average ([plus or minus] SD) of 50.3 [plus or minus] 11.2%, and phosphorus resorption efficiency (PRE) varied among species between 46% and 82%, with a mean ([plus or minus] SD) of 68.4 [plus or minus] 6.9%, suggesting that nutrient resorption is a vital nutrient conservation strategy in this ecosystem. In addition, NRE and PRE differed significantly among the dominant plant growth forms in this sandy grassland. NRE for N-fixing species and graminoids were significantly lower relative to NRE for shrubs and forbs, but mean PRE of graminoids was significantly higher than those of N fixers, shrubs and forbs. These data give indirect evidence that the differentiation of N and P conservation serve as an important mechanism permitting the co-existence of growth forms in arid systems.

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Leaf nitrogen resorption pattern along habitats of semi-arid sandy land with different nitrogen status

Luo Y., Zhao X., Zuo X., Zhang J., Liu R., Wang S.

Polish Journal of Ecology

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2010

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Vol. 58, nr 4

707-716

EN

To assess nitrogen (N) resorption patterns in semi-arid sandy land, N concentrations in green leaves (N[g]) and senesced leaves (N[s]) of 35 species of shrubs and herbages were measured along habitats of decreasing soil total N (0.54 to 0.041 g g[^-1] d.w. of top soil level) in Horqin Sandy Land (Inner Mongolia, China). These habitats are following: inter-dune grassland (IDG), fixed sand dune (FD), semi-fixed sand dune (SFD), semi-mobile sand dune (SMD), and mobile sand dune (MD) were considered. Results showed that Ng and Ns (i.e. nitrogen resorption proficiency, NRP) increased and leaf nitrogen use efficiency (NUE) decreased significantly with increasing soil N status across the above habitas, but nitrogen resorption efficiency (NRE) was not affected. The levels of N[g], N[s] and NUE experience two stages across habitats: first, there were low N[g] and N[s and high NUE in MD and SMD; second, there were high N[g] and N[s] and low NUE in IDG, FD and SFD. Plants from IDG, FD and SFD had incomplete N resorption during foliar senescence, but plants from MD and SMD had complete N resorption. Leaf NRE was determined by life forms which had no significant effect on N[g] but on N[s] and NUE. For all plants in the five habitats, NRE and NUE decreased with the sequence of grass, herb, shrub, while Ns showed a contrary tendency. Plants from strong N limitation habitats did not show higher NRE, but showed higher NRP and leaf NUE, so NRP was a more sensitive indicator of changes in N status than NRE. In conclusion, Leaf N resorption patterns were mainly determined by soil N status across habitats, and there were some consistent patterns among life forms.