Decomposition Enzyme Activities Research Articles

Plant facilitation improves carbon production efficiency while reducing nitrogen input in semiarid agroecosystem

It is critical to reduce carbon (C) emission and nitrogen (N) input in agroecosystems under a changing climate. If crop diversification is introduced, interspecific plant–plant interactions as an effective pathway may achieve this goal. However, the related process and its mechanism are poorly understood. A two-year field study was conducted to explore the effects of intercropping systems including soybean-maize, soybean- wheat and maize-wheat on the land equivalent ratio (LER), nitrogen use efficiency (NUE), seasonal carbon emission, and soil properties in a typical semiarid environment. Three N rates (N1: 150 kg ha−1, N2: 225 kg ha−1, N3: 300 kg ha−1) were applied. The result indicated that the intercropping with soybean significantly increased system productivity with LER > 1, showing a typical plant–plant facilitation. However, the LER of maize–wheat intercropping was significantly lower than 1, representing interspecific competition. With the increasing N rate, the productivity of monoculture wheat or maize was evidently promoted. Particularly, the productivity under N2 and N3 remained at a similar level due to interspecific facilitation. This trend was mechanically driven by the improved N uptake (NLER > 1) and NUE under the presence of interspecific facilitation. Critically, interspecific facilitation was observed to promote carbon emissions (CE) by 4.0%-6.3%, since root input, microbial activities and the C&N decomposition enzyme activities were significantly enhanced. To say, interspecific facilitation evidently enhanced carbon emission efficiency (Yield/CE) whereas interspecific competition turned to lower it. To sum up, plant facilitation improved crop productivity and carbon emission efficiency by reducing N input. Our findings provided a new insight into the exploration of green solution in terms of reducing emissions and increasing efficiency, as well as lowering N fertilizer application in the natural and agricultural ecosystems.

Rapid Shifts in Soil Nutrients and Decomposition Enzyme Activity in Early Succession Following Forest Fire

While past research has studied forest succession on decadal timescales, ecosystem responses to rapid shifts in nutrient dynamics within the first months to years of succession after fire (e.g., carbon (C) burn-off, a pulse in inorganic nitrogen (N), accumulation of organic matter, etc.) have been less well documented. This work reveals how rapid shifts in nutrient availability associated with fire disturbance may drive changes in soil enzyme activity on short timescales in forest secondary succession. In this study, we evaluate soil chemistry and decomposition extracellular enzyme activity (EEA) across time to determine whether rapid shifts in nutrient availability (1–29 months after fire) might control microbial enzyme activity. We found that, with advancing succession, soil nutrients correlate with C-targeting β-1,4-glucosidase (BG) EEA four months after the fire, and with N-targeting β-1,4-N-acetylglucosaminidase (NAG) EEA at 29 months after the fire, indicating shifting nutrient limitation and decomposition dynamics. We also observed increases in BG:NAG ratios over 29 months in these recently burned soils, suggesting relative increases in microbial activity around C-cycling and C-acquisition. These successional dynamics were unique from seasonal changes we observed in unburned, forested reference soils. Our work demonstrates how EEA may shift even within the first months to years of ecosystem succession alongside common patterns of post-fire nutrient availability. Thus, this work emphasizes that nutrient dynamics in the earliest stages of forest secondary succession are important for understanding rates of C and N cycling and ecosystem development.

Soil aggregate size distribution mediates microbial climate change feedbacks

Soil carbon stabilization is known to depend in part on its distribution in structural aggregates, and upon soil microbial activity within the aggregates. However, the influence of climate change on continued soil C storage within aggregates of different size classes is unknown. In this study, we applied a modified dry-sieving technique to separate bulk soil into three fractions (>1 mm large macroaggregate; 0.25–1 mm small macroaggregate; <0.25 mm microaggregate), and measured the activities of seven microbial enzymes involved in the cycling of C, N, and P, in the context of a long-term elevated CO2 and warming experiment. Significant effects of aggregate size were found for most enzyme activities, enzyme stoichiometry, and specific enzyme activities (per unit of microbial biomass), suggesting that aggregate size distribution mediates microbial feedbacks to climate change. C decomposition enzyme activities, the ratios of total C:N and C:P enzyme activity, and the specific enzyme activity for C decomposition were significantly higher in the microaggregates across climate treatments. However, specific enzyme activity for N decomposition was significantly higher in macroaggregates. Increased specific enzyme activity for C decomposition under both elevated CO2 and warming suggests that these climate changes can enhance microbial ability to decompose soil organic matter (SOM). Moreover, changes in the enzyme C:N:P stoichiometry suggest that soil microorganisms may be able to adjust nutrient acquisition ratios in response to climate change. Our study suggests that identifying and modeling aggregate size as a function of SOM decomposition could improve our mechanistic understanding of soil biogeochemical cycling responses to climate change.

Sucrose Accumulation and Key Enzyme Activities in Different Parts of Seed in Vegetable Soybean

Three vegetable soybean varieties(lines)with different soluble sugar contents were grown in field condition.Sucrose contents and four critical enzymes activities in different parts of seed were analyzed at R5.5,R6,R6.2,R6.5,and R7 stages,respectively.Sucrose contents of different seed parts increased at early seed filling stage and then decreased at late stage with the peak value at R6.2 stage.Sucrose content in hypocotyl was 57.6%,53.6%,44.2% greater than that of cotyledon,and 71.6%,75.3%,73.6% greater than that of seed coat at R6.2 stage for the three varieties(lines),respectively.The cotyledon contributed90% dry weight to the total seed dry weight,and thus the sucrose content of the whole seed was primarily determined by sucrose content in cotyledon.Cotyledon had the highest activity of sucrose phosphate synthase(SPS).The cotyledon SPS activity of cv.121 was much higher than those of the other two varieties(lines).The sucrose synthase(SS)activity of different seed parts was higher in early seed filling stage than in late filling stage.The highest value of SS activity was observed in hypocotyl at R5.5 stage.Greater differences were found between acid invertase(AI)and neutral invertase(NI)activities.NI activity was higher in early seed filling stage and then decreased till R7 stage.Significant differences were observed for AI activities among three seed parts at the same seed filling stage but there were no differences for NI activities.AI activity in seed coat was much higher than those in hypocotyl and cotyledon.Negative relationship was found between AI activity and sucrose content in seed coat(r = –0.59**).The correlation analysis between sucrose accumulation and four critical enzymes activities showed that seed sucrose content was not controlled dominantly by one enzyme.The difference between sucrose synthesis enzyme activity(SPS)and sucrose decomposition enzyme activity(SS+AI+NI)was positively correlated with seed sucrose accumulation(r=0.53**).