Soil Microbial Biomass For Larix Gmelinii Forests Transplanted From A Latitudinal Transect

Soil microbial biomass is the most active and sensitive component of soil organic matter to environmental changes.We transplanted an 8-year-old Dahurian larch(Larix gmelinii Rupr.) plantation each from four sites,i.e.Tahe(52°31′N,124°39′E),Songling(50°43′N,124°25′E), Sunwu(49°13′N,127°12′E) and Dailing(47°05′N,128°54′E),comprising a latitudinal transect across the distribution range of the larch in northeastern China to its southern distribution boundary to mimic climate warming.Three years after the transplanting,we measured soil microbial biomass carbon(MBC) and nitrogen(MBN) of the four treatments with a fumigation-extraction method in 2007,which to examine temporal dynamics and impact factors of soil microbial biomass.The MBC and MBN transplanted from four sites reached the peak of the whole year before soil thawing(the MBC for the Dailing,Sunwu,Songling and Tahe peaked 2429.74,1729.75, 2818.28 and 977.56 mg·kg^-1,respectively,while the MBN peaked 388.75,209.78,320.90 and 139.07 mg·kg^-1,respectively),rapidly declined at the beginning of soil thawing,varied little and maintained at a lower level during the soil freeze-thawing period.The MBC of the lower latitudinal soils tended to recover faster at the end of soil thawing.The dynamics of MBC were different among four treatments during the growing season,but the fluctuations of MBN were no significant.Soil water content(W_s) and soil temperature(T_s) were the important factors affected the temporal patterns of MBC and MBN,but the influential extent depended on season.There was a positive correlation between W_s and MBC,MBN in te whole year(Spearman correlations were 0.590 and 0.433,respectively).The relationship between soil microbial biomass(MBC, MBN) and T_s at the early stage of soil thawing was negative,and was nonsignificant after soil thawing and during the growing season.A significantly positive correlation between MBC,MBN and soil total organic carbon (TOC),total nitrogen(TN) were found in this study(Spearman correlations of MBC and TOC,TN were 0.720 and 0.484,respectively,while that of MBN and TOC,TN were 0.725 and 0.533,respectively).The relationship of MBC against dissolved organic carbon(DOC) was negative,Spearman correlation was -0.173.And Spearman correlations of MBN against NH₄⁺-N,NO₃^--N were 0.341 and 0.339,respectively,which were significantly positive.The MBC,MBN,TOC and TN were significantly affected by global warming.They decreased with increasing latitudes before transplanting.The TOC and TN of four treatments tended to consistency after transplanting,and MBC of the transplanted sites were much smaller than that of the original sites. The mean values of MBC and MBN differed significantly among the four treatments after 3 years' adaption(MBC,P<0.01,F=13.621;MBN:P<0.01,F=4.621),tending to decrease with increasing latitudes and soil depth.The MBC for the Dailing,Songling,Sunwu and Tahe treatments averaged 1026.08±78.45,709.29±51.02,666.87±76.24 and 452.72±41.05 mg·kg^-1,respectively,while the MBN averaged 105.42±10.97,75.28±5.56,85.54±8.43 and 64.88±5.27 mg·kg^-1,respectively.In addition to the influences of environmental factors on soil microbial biomass and its temporal patterns for the four treatments under similar soil substrates and warming climate,further studies are needed on the effect of the intrinsic properties of the microbial communities from the latitudinal transect.