ABSTRACT
This study aimed to examine the responses of persistent soil seed bank to future precipitation reduction of global climate change in the forest-steppe ecotone of Hulunbuir. Samples of soil seed bank were collected from 0-10 cm soil layer along a precipitation gradient. We examined the density, species composition, diversity of seed bank and their relationship with vegetation. Structural equation model was used to explore the direct impact of annual precipitation on soil seed bank and the indirect impact through vegetation, soil nitrogen, soil phosphorus, and soil pH. The results showed that seed bank density and species richness were negatively correlated with annual precipitation. The species diversity of soil seed banks in grasslands was higher than that in forests. The similarity between soil seed bank and vegetation was generally low. The results of structural equation model showed that the effects of annual precipitation on seed bank density and species richness were negative, with the standard path coefficients of -0.051 and -0.122, respectively. The direct effect of annual precipitation on seed bank density and species richness were positive. Precipitation had indirect and positive effect on seed bank density and species richness through soil nitrogen, a significantly indirect negative effect on seed bank species richness through soil pH and soil available phosphorus, and a significantly indirect negative effect on seed bank density through soil pH. The reduction of precipitation under furture climate change might alter the hedging strategies of plants. The persistent soil seed bank in the forest-steppeecotone had a potential buffering effect against future precipitation reduction.
Subject(s)
Seed Bank , Soil , Ecosystem , Forests , Nitrogen , Phosphorus , Seeds/physiology , Soil/chemistryABSTRACT
Nitrogen is the most limiting nutrient for ecosystems. The natural abundance of δ15N (15N/14N) can efficiently indicate ecosystem nitrogen cycling processes. We investigated the interannual variations in natural abundance of δ15N in soil-plant system and soil net nitrogen mineralization in a meadow steppe of Inner Mongolia. Results across the four sampling years (2017-2020) showed that the content of soil NO3--N (9.83-14.79 mg·kg-1) was significantly higher than that of NH4+-N (3.92-5.00 mg·kg-1) and that δ15N value of soil NH4+ (13.3-18.3) was significantly higher than that of NO3-(3.76-6.14). The δ15N value of soil NO3- was negatively correlated with soil NO3- content. The δ15N value of soil NH4+ was relatively higher in the dry years, while the δ15N value of soil NO3- significantly decreased in the wetter and drier years. Soil net mineralization and ammonification rates were significantly higher in the dry years than that of the wet years, while soil nitrification rates showed no correlation with annual precipitation. The δ15N values of plants were not related to that of soils, but nega-tively correlated with plant nitrogen content. Both δ15N values and nitrogen contents were significantly and positively correlated between the leguminous and non-leguminous plants, suggesting that legume could facilitate nitrogen uptake of non-leguminous plants. These results could provide supporting data for nitrogen cycling and their responses to changes in precipitation in grassland soil-plant systems.
Subject(s)
Ecosystem , Soil , China , Grassland , Nitrogen/analysis , Nitrogen Isotopes/analysis , PlantsABSTRACT
Reasonable nutrient and water management is effective ways to improve productivity and biodiversity of degraded grasslands. However, little is known about the effects of nutrient and water addition on soil inorganic phosphorus (P) fractions in old-field grasslands. Based on a field experiment with nutrient addition (N: 10 g·m-2·a-1, P: 10 g·m-2·a -1) and water addition (180 mm water irrigated during plant growing season) in Duolun County, Inner Mongolia in 2005, we examined the changes of inorganic P fractions and Olsen-P contents in the topsoil (0-10 cm). Results showed that 11-year P addition significantly increased total inorganic P (TIP) content, and that exogenous P was mostly transformed into calcium phosphate (Ca-P: 62.6%-69.2%), and then into aluminium phosphate (Al-P: 19.9%-25.1%), ferric phosphate (Fe-P) and occluded P (O-P). Phosphorus incorporated with nitrogen (N) addition significantly increased Fe-P and Al-P contents by declining soil pH and activating Fe3+ and Al3+ in soil. Water addition alone significantly increased Fe-P, Al-P, and decalcium phosphate (Ca10-P) fractions, and the contents of Fe-P, Al-P, octacalcium phosphate (Ca8-P), and Ca10-P were greater in P incorporated with water treatment than in P addition alone. There was no difference of each inorganic P fraction between P incorporated with N and water treatment and P incorporated with N treatment. Phosphorus and P incorporated with N additions significantly increased soil Olsen-P content, while water addition significantly decreased soil Olsen-P content under P addition alone and P incorporated with N treatment. In the calcareous soils, calcium superphosphate addition could enhance soil inorganic P pool through increasing Ca-P fraction.
Subject(s)
Grassland , Soil , Nitrogen , Nutrients , Phosphorus/chemistry , Soil/chemistryABSTRACT
The continuing nitrogen (N) deposition observed worldwide alters ecosystem nutrient cycling and ecosystem functioning. Litter decomposition is a key process contributing to these changes, but the numerous mechanisms for altered decomposition remain poorly identified. We assessed these different mechanisms with a decomposition experiment using litter from four abundant species (Achnatherum sibiricum, Agropyron cristatum, Leymus chinensis and Stipa grandis) and litter mixtures representing treatment-specific community composition in a semi-arid grassland under long-term simulation of six different rates of N deposition. Decomposition increased consistently with increasing rates of N addition in all litter types. Higher soil manganese (Mn) availability, which apparently was a consequence of N addition-induced lower soil pH, was the most important factor for faster decomposition. Soil C : N ratios were lower with N addition that subsequently led to markedly higher bacterial to fungal ratios, which also stimulated litter decomposition. Several factors contributed jointly to higher rates of litter decomposition in response to N deposition. Shifts in plant species composition and litter quality played a minor role compared to N-driven reductions in soil pH and C : N, which increased soil Mn availability and altered microbial community structure. The soil-driven effect on decomposition reported here may have long-lasting impacts on nutrient cycling, soil organic matter dynamics and ecosystem functioning.
Subject(s)
Ecosystem , Nitrogen , Grassland , Plant Leaves , Plants , Poaceae , SoilABSTRACT
Frequent mowing and nitrogen enrichment can lead to the degradation of grassland ecosystem. It remains largely unknown that how the soil microbial characteristics, important bio-indicators of soil quality, respond to mowing and nitrogen enrichment. In this study, using a field experiment established in the meadow steppe in Hulunber, Inner Mongolia, we explored the responses of soil properties, microbial biomass, soil respiration, and soil enzyme activities to mowing and nitrogen addition during growing seasons. Mowing significantly reduced microbial biomass carbon, nitrogen and phosphorus, and soil respiration (basal respiration and substrate induced respiration), which might be caused by the moisture- and carbon-limitation. Mowing significantly reduced activities of the enzymes involved in nitrogen acquisition (N-acetyl-ß-D-glucosaminidase) and phosphorus acquisition (acidic phosphomonoesterases), which supports the resource allocation theory. Soil pH was significantly reduced by N addition. However, microbial biomass showed no significant response to nitrogen input, implying that soil acidification induced by nitrogen inputs was not profound enough to affect microbial biomass. Nitrogen addition did not affect soil respiration and microbial enzymatic activities, inconsistent with results from most of previous studies conducted in typical steppe. Combination of mowing and nitrogen addition reduced the activity of acidic phosphomonoesterases, which might be due to the increased phosphorus availability under the combined treatment. Combination of mowing and nitrogen addition reduced microbial biomass phosphorus, but increased soil available phosphorus, corresponding to the lowered activity of acidic phosphomonoesterases under the combined treatment. Microbial biomass carbon, nitrogen and phosphorus, and soil respiration peaked in July, which was associated with the high temperature and precipitation in summer. Soil enzymatic activities were higher in the spring and summer than in the late growing season. In summary, our results indicated that mowing would result in the imbalance of soil nutrients and intensify the risk of grassland degradation. In contrary, nitrogen addition exerted no effects on microbial biomass and activity.
Subject(s)
Ecosystem , Nitrogen , Soil Microbiology , Soil , Biomass , Carbon , China , PoaceaeABSTRACT
We summarized the effects of fertilization and water addition on some soil properties and plant community characteristics in a long-term field experiment established in 2005 in a degraded grassland in Duolun, Inner Mongolia, China. The results showed that nitrogen (N) addition resulted in surface soil acidification and decreased acid buffering capacity, increased the availability of carbon (C), N, phosphorus (P), sulfur (S) and DTPA-extractable iron (Fe), manganese (Mn), and copper (Cu) contents, depleted the sum of base cations calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na), decreased the diversity of soil microbial community. Nitrogen addition enhanced the uptake of N, P, S, K, Mn, Cu and Zn by plants, while inhibited plant Fe uptake, but with no effect on the uptake of Ca or Mg. Nitrogen addition increased aboveground net primary productivity (ANPP) but declined plant species diversity and community stability. Phosphorus addition alone increased total P and Olsen-P contents and fungal abundance in the surface soil, and improved N, P and S uptake by leaves, but had no significant influence on other soil basic chemical properties, ANPP, and plant species diversity. Water addition could improve the resistance of plant community, but its contribution to ANPP was limited by soil N availa-bility. Water addition could buffer soil acidification and the decline of microbial and plant diversity induced by N addition. Under the treatments of N and water addition or P and water addition, the diversity and function of soil microorganisms were affected by plant community structure and function. Long-term controlled field experiments were useful for understanding ecosystem structure and functions of grasslands. However, to uncover the underlying mechanisms in grassland ecosystem ecology, single-site experiments should be incorporated with multiple-site controlled field experiments in different regions. More attentions should be paid to the linkage of above- and below-ground ecological processes.
Subject(s)
Agriculture , Fertilizers , Grassland , Soil , China , Ecosystem , Nitrogen , Plants , WaterABSTRACT
In this study, we measured the responses of soil bacterial diversity and community structure to nitrogen (N) and water addition in the typical temperate grassland in northern China. Results showed that N addition significantly reduced microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) under regular precipitation treatment. Similar declined trends of MBC and MBN caused by N addition were also found under increased precipitation condition. Nevertheless, water addition alleviated the inhibition by N addition. N addition exerted no significant effects. on bacterial α-diversity indices, including richness, Shannon diversity and evenness index under regular precipitation condition. Precipitation increment tended to increase bacterial α-diversity, and the diversity indices of each N gradient under regular precipitation were much lower than that of the corresponding N addition rate under increased precipitation. Correlation analysis showed that soil moisture, nitrate (NO3(-)-N) and ammonium (NH4+-N) were significantly negatively correlated with bacterial evenness index, and MBC and MBN had a significant positive correlation with bacterial richness and evenness. Non-metric multidimensional scaling (NMDS) ordination illustrated that the bacterial communities were significantly separated by N addition rates, under both water ambient and water addition treatments. Redundancy analysis (RDA) revealed that soil MBC, MBN, pH and NH4+-N were the key environmental factors for shaping bacterial communities.
