陕北黄土丘陵区撂荒群落土壤养分与地上生物量空间异质性

Spatial heterogeneity of soil nutrients and aboveground biomass in abandoned old-fields of Loess Hilly region in Northern Shaanxi,China

应用地统计学方法，研究了群落尺度上陕北黄土丘陵区不同演替阶段猪毛蒿、长芒草和达乌里胡枝子3种撂荒群落土壤全氮、全磷和地上生物量的空间异质性。利用基于距离矩阵的Mantel偏相关方法分析了群落地上生物量与土壤全氮、全磷在不同尺度上的相互关系，分析了土壤全氮、全磷及群落自身的空间过程对群落地上生物量空间分布的解释程度。结果表明：（1）猪毛蒿、长芒草和达乌里胡枝子3种群落土壤全氮含量空间自相关性较差，而全磷自相关性较好，不同深度的土壤全氮含量其空间异质性大小也有所差别。3种群落0—20cm全氮的空间变异性大小为：达乌里胡枝子〉长芒草〉猪毛蒿群落；20—40cm为：长芒草〉达乌里胡枝子〉猪毛蒿群落。即土壤表层全氮含量为撂荒年限越长空间变异性越大，而亚表层全氮含量则是演替中期空间异质性较大，演替前后期较小。3种群落0—20cm、20—40cm全磷含量也是演替中期空间异质性较大，而前后期较小。（2）3种群落地上生物量空间自相关性以长芒草群落为最小，并且空间异质性大小为猪毛蒿〉达乌里胡枝子〉长芒草群落；猪毛蒿群落地上生物量与土壤全氮在小尺度上（0．71m）为显著正相关，与全磷相关性也较好，为负相关，在19．80—20．51m尺度上与全磷为显著负相关。达乌里胡枝子群落地上生物量与全磷在7．07—20．51m尺度上为显著正相关，在小尺度上（0．71m）正相关性也较好。长芒草群落地上生物量与土壤全氮、全磷相关性在各个尺度上都不显著，只在小尺度上与全氮负相关性较好。（3）土壤氮和磷，对达乌里胡枝子群落地上生物量的解释较好，约为19．59％，猪毛蒿次之，长芒草群落最小。群落本身的空间过程对猪毛蒿群落的解释程度最高，约为5．42％，其次为达乌里胡枝子，长芒草最小。

Spatial heterogeneous characteristics of aboveground biomass and total soil nitrogen and phosphorus in 0- 20cm and 20 - 40cm depths of three different successional stage old-field communities, Artemisia scoparia （ early stage）, Stipa bungeana （mid stage ） and Lespedeza dahurica （later stage）, were analyzed using geostatistical methods. The correlations of aboveground biomass and total nitrogen and phosphorus at different scales were computed using partial Mantel analyses based on distance matrices. Moreover, the variations of aboveground biomass were partitioned into community space process and environment components （including soil nitrogen and phosphorus）. The results show that： （1） total phosphorus of the three communities has relatively larger spatial autoeorrelation coefficients than that of total nitrogen. Total nitrogen of different layers also has different spatial heterogeneous extent. The variability of total nitrogen in 0 - 20cm ranked as ： L. dahurica 〉 S. bungeana 〉 A. scoparia, in 20 - 40cm ： S. bungeana 〉 L. dahurica 〉 A. scoparia, so we infer that the variability of total nitrogen in the top layer increases as succession occurs, while in subsoil, the variability of mid-succession stage is greater than that of earlier and later succession stages. The total phosphorus in both layers also has greater variability in mid-succession stage and smaller values in earlier and later succession stages. （2） Aboveground biomass of the three communities has different spatial autocorrelation coefficients, S. bungeana has the smallest value. The variability were ranked as A. scoparia 〉 L. dahurica 〉 S. bungeana. The partial Mantel correlgram of A. scoparia community show significant positive partial correlation at the small scale （0.71m） between aboveground biomass and total nitrogen and relatively good negative correlation at the small scale （0.71m） with significant correlation between aboveground biomass and total phosphorus. For L. dahurica community, significant positive correlation between aboveground biomass and total phosphorus occurred at 7.07 - 20.51m scale, small scale （0.71m） also has great positive correlation. No significant correlation was found for S. bungeana community with either total nitrogen, or total phosphorus, （only at small scale, the spatial heterogeneity of L. dahurica aboveground biomass, 2.75 % of A. scoparia, and 1.95 % S. bungeana. The space process accounted for about 5.42% of the heterogeneity of A. scoparia, 1.79% of L. dahurica, and 1. 16% of S. bungeana.