Aggregate-associated changes in nutrient properties,microbial community and functions in a greenhouse vegetable field based on an eight-year fertilization experiment of China

Soil aggregation,microbial community,and functions(i.e.,extracellular enzyme activities;EEAs)are critical factors affecting soil C dynamics and nutrient cycling.We assessed soil aggregate distribution,stability,nutrients,and microbial characteristics within>2,0.25-2,0.053-0.25,and<0.053 mm aggregates,based on an eight-year field experiment in a greenhouse vegetable field in China.The field experiment includes four treatments:100%N fertilizer(CF),50%substitution of N frtilizer with manure(M),straw(S),and manure plus straw(MS).The amounts of nutrient(N,P20,and K20)input were equal in each treatment.Results showed higher values of mean weight diameter in organic amended soils(M,MS,and S,2.43-2.97)vs.CF-amended soils(1.99).Relative to CF treatment,organic amendments had positive effects on nutrient(i.e.,available N,P,and soil organic C(SOC))conditions,microbial(e.g,bacterial and fungal)growth,and EEAs in the>0.053 mm aggregates,but not in the<0.053 mm aggregates.The 0.25-0.053 mm aggregates exhibited better nutrient conditions and hydrolytic activity,while the<0.053 mm aggregates had poor nutrient conditions and higher oxidative activity among aggregates,per SOC,available N,available P,and a series of enzyme activities.These results indicated that the 0.25-0.053 mm(<0.053 mm)aggregates provide suitable microhabitats for hydrolytic(oxidative)activity.Interestingly,we found that hydrolytic and oxidative activities were mainly impacted by fertilization(58.5%,P<0.01)and aggregate fractions(50.5%,P<0.01),respectively.The hydrolytic and oxidative activities were significantly(P<0.01)associated with nutrients(SOC and available N)and pH,electrical conductivity,respectively.Furthermore,SOC,available N,and available P closely(P<0.05)afected microbial communities within>0.25,0.25-0.053,and<0.053 mm aggregates,respectively.These findings provide several insights into microbial characteristics within aggregates under dfferent frilization modes in the greenhouse vegetable production system in China.

Invasive weed disrupts facilitation of nutrient uptake in grass-clover assemblage

Nutrient constraints in low-fertility soil were modified by different species combinations.Grass-clover assemblages benefited both species in terms of nutrient procurement.Interplay of competition and facilitation is demonstrated.An invasive weed removed essential nutrients from the grazing cycle.To investigate the interplay of competition and facilitation between plants in low-fertility pasture grasslands of New Zealand,we compared nutrient uptake and acquisition of key nutrients of three species from different func-tional groups.Combinations of Pilosella officinarum(mouse-eared hawk-weed,an invasive weed),Trifolium repens(white clover,a nitrogen fixer)and Dactylis glomerata(cocksfoot,a pasture grass)were planted into a soil with low-to-deficient concentrations of key nutrients.Highest yields were achieved by the grass growing alone but,when the clover and grass had grown together,there were complementary benefits in terms of procurement of a wide range of nutrients from soil despite lower root biomass.The inva-sive weed negated these benefits,and soil nutrients were exploited less efficiently when Pilosella had grown alone or in a mixture with the other species.Competition from the weed removed the benefits of grass-legume coexistence.These findings are interpreted to suggest that requirements for legumes to be the main source of nitrogen in pasture grasslands may be compromised unless competitive weeds are controlled to avoid disrupted procurement of key nutrients.It is likely these constraints to nutrient procurement would similarly impact conservation grasslands.