Carbon,Nitrogen And Phosphorus Distribution Within Soil Water-stable Aggregates As Affected By Experimental Warming In A Tibetan Alpine Meadow

In terrestrial ecosystems,the cycles of carbon(C),nitrogen(N),and phosphorus(P)in biogeochemical cycles are combined with biochemical reactions in primary production,respiration,and decomposition processes.Among them,N and P are the most important nutrients that limit the growth of different plants and organisms.The study of soil organic carbon(SOC),N,P responses to climate warming in a Tibetan alpine meadow is of great significance for global carbon pools,soil fertility,vegetation productivity,and community structure.The alpine meadow soil in the Tibetan Plateau contains a large amount of SOC,which is highly vulnerable to climate change,therefore,it has been the focus of scientists' research in recent decades.However,how climate warming affects the SOC,N,P content and stability in soil and its aggregates remains unclear.In this study,open-top chambers(OTCs)were used to experimental temperature-increasing settings,and the alpine meadow soil and water-stable aggregates soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP)nutrients respond to climate warmingin a Tibetan alpine meadow were studied by the physical grouping of agglomerates and the organic matter density groupings.The experimental temperature increase test involved three treatments,namely,unwarmed control(CK),winter warming(WW,3 yr),and year-round warming(YW,5 yr).The main results were as follows:1?The aggregate composition of alpine meadow soil on the Tibetan Plateau is dominated by macroaggregates(M)and free microaggregates(Fm),and soil organic carbon(SOC),total nitrogen(TN)and total phosphorus(TP)stored in M had the highest storage and contribution to all soil C,N and P,and the <0.053 mm NA-silt+clay had the lowest grain size.2?Winter warming(WW,3 yr)and year-round warming(YW,5 yr)have affected the stability of aggregates,significantly increased the mass fraction of NA-silt+clay grades,and the proportion of M and Fm mass decreased trend.Experimental warming(including WW and YW)significantly reduced the mass fraction of POM inside free microaggregates(Fm-POM),YW significantly reduced the mass fraction of POM inside occluded microaggregaters(mM-POM).3?The experimental warming had no significant effect on the SOC content,TN content,and C:N,C:P ratio of the soil,but reduced the total soil TP content,Among them,the TP content of WW was significantly different from that of CK.4?The effect of experimental warming on the storage of SOC,TN and TP in soil aggregates with different particle sizes.(1)The C of free microaggregates is sensitive to the increase of year-round warming,YW significantly reduces SOC storage of Fm and non-occluded fine POM inside free microaggregates(Free(f)POM),POM inside free microaggregates(Fm-POM),and Silt-and clay-sized fractions inside free microaggregates(Fm-silt+clay).The experimental warming significantly increased the storage of NA-silt+clay fractional SOC.(2)The N of free microaggregates is sensitive to the experimental temperature increase,experimental warming significantly reduced the TN storage of Fm and Fm-POM,and significantly increased the TN storage of NA-silt+clay grades.(3)Experimental warming significantly increased NA-silt+clay grain TP storage.(4)The experimental warming significantly reduced the C:N and C:P ratios of the NA-silt+clay and the C:P ratio of the Fm particle size.In summary,the experimental warming had no significant effect on the SOC and TN content of alpine meadow soil in the Tibetan Plateau,but reduced the TP content in the soil.C and N in the free microaggregates are sensitive to the experimental temperature increase,simulated warming significantly reduces the SOC and TN storage of free microaggregates,and significantly increases the non-aggregated silt+clay size SOC,TN and TP storage,the non-aggregated silt+clay size C:N and C:P ratios are reduced.The experimental warming has an effect on the stability of soil aggregates.The effect of experimental warming on the distribution of C,N,and P in aggregates of different sizes led to the net change of C,N,and P in a Tibetan alpine meadow.Compared with the three-year warming in winter,the five-year year-round warming has more significant effects on C,N,and P in soil aggregates.Under the background of long-term climate warming,climate warming may have a negative effect on the C reservoir of alpine meadow soil in the Tibetan Plateau.