Lespedeza Davurica Research Articles

Effects of nitrogen addition and Bothriochloa ischaemum and Lespedeza davurica mixture on plant chlorophyll fluorescence and community production in semi-arid grassland.

Grass-legume mixture can effectively improve productivity and stimulate overyielding in artificial grasslands, but may be N-limited in semi-arid regions. This study investigated the effects of N addition on chlorophyll fluorescence and production in the grass-legume mixtures community. An N addition experiment was conducted in the Bothriochloa ischaemum and Lespedeza davurica mixture community, with seven mixture ratios (B0L10, B2L8, B4L6, B5L5, B6L4, B8L2, and B10L0) according to the sowing abundance of B.ischaemum and L.davurica and four N addition levels, N0, N25, N50, and N75 (0,25,50,75kgNhm-2 a-1), respectively. We analyzed the response of chlorophyll fluorescence parameters of the two species, the rapid light-response curves of chlorophyll fluorescence, as well as aboveground biomass (AGB) and overyielding. Our results showed that the two species showed different photosynthetic strategies, with L.davurica having significantly higher initial fluorescence (Fo), effective photochemical quantum yield of PSII (ΦPSII), and coefficient of photochemical fluorescence quenching (qP) than B. ischaemum, consisting with results of rapid light-response curves. N addition and mixture ratio both had significant effects on chlorophyll fluorescence and AGB (p<0.001). The ΦPSII and qP of L.davurica were significantly lowest in B5L5 and B6L4 under N addition, and the effect of N varied with mixture ratio. The photosynthetic efficiency of B. ischaemum was higher in mixture than in monoculture (B10L0), and ΦPSII was significantly higher in N50 than in N25 and N50 at mixture communities except at B5L5. The community AGB was significantly higher in mixture communities than in two monocultures and highest at B6L4. In the same mixture ratio, the AGB was highest under the N50. The overyielding effects were significantly highest under the N75 and B6L4 treatments, mainly attributed to L.davurica. The partial least squares path models demonstrated that adding N increased soil nutrient content, and complementary utilization by B.ischaemum and L.davurica increased the photosynthetic efficiency. However, as the different photosynthetic strategies of these two species, the effect on AGB was offset, and the mixture ratio's effects were larger than N. Our results proposed the B6L4 and N50 treatments were the optimal combination, with the highest AGB and overyielding, moderate grass-legume ratio, optimal community structure, and forage values.

Morphological Study on the Differentiation of Flower Buds and the Embryological Stages of Male and Female Floral Organs in Lespedeza davurica (Laxm.) Schindl. cv. JinNong (Fabaceae).

Lespedeza davurica (Laxm.) is a leguminous plant with significant ecological benefits, but its embryonic development mechanism remains unclear. We investigated the flower bud differentiation, megaspore and microspore formation, gametophyte development, and embryo and endosperm development in L. davurica. Our aim was to elucidate the relationship between the external morphology and internal development processes of male and female floral organs during growth, as well as the reproductive factors influencing fruiting. The results indicated that although the pistil develops later than the stamen during flower bud differentiation, both organs mature synchronously before flowering. L. davurica pollen exhibits three germination grooves, a reticulate outer wall, and papillary structures on the anther surface. In vivo pollination experiments revealed abnormal spiral growth of L. davurica pollen tubes within the style and the occurrence of callus plugs, which may reduce the seed setting rate. The anther wall development follows the dicotyledonous type, with tetrads formed through microspore meiosis exhibiting both left-right symmetry and tetrahedral arrangements. L. davurica has a single ovule, and the embryo sac develops in the monosporic polygonum type. After dormancy, the zygote undergoes multiple divisions, progressing through spherical, heart-shaped, and torpedo-shaped embryo stages, culminating in a mature embryo. A mature seed comprises cotyledons, hypocotyl, embryo, radicle, and seed coat. Phylogenetic tree analysis reveals a close genetic relationship between L. davurica and other leguminous plants from the genera Lespedeza and Medicago. This study provides valuable insights into the regulation of flowering and hybrid breeding in leguminous plants and offers a new perspective on the development of floral organs and seed setting rates.

Aboveground biomass determines canopy rainfall interception loss in Semiarid Grassland Communities

AbstractCanopy rainfall interception is one key hydrological process, affecting rainwater redistribution and effectiveness in semiarid regions. Canopy rainfall interception loss is jointly influenced by meteorology, vegetation and topography. The canopy water storage capacity (S), rainfall interception depth (Im) and ratio (I%) and vegetation characteristics, together with topographic factors of three grassland communities (dominated by Bothriochloa ischaemum, Lespedeza davurica and Artemisia gmelinii, respectively) were investigated on the Loess Plateau of China during the main growing season (June to September). Results showed that Im ranged from 0.55 to 0.89 mm and I% ranged from 6.14% to 12.1%, with the maximum values occurring in August for three communities, and A. gmelinii community had the largest Im (0.89 mm) and I% (12.1%). The Im and I% were positively correlated with aboveground biomass (AGB), coverage (Cov), leaf area index (LAI), community‐weighted mean height (CWMH) and altitude (Alt), but negatively correlated with slope degree and rainfall intensity (RI). Hierarchical partitioning analysis (HPA) showed that AGB had the highest contribution for Im (20.3%), while Alt had the highest contribution for I% (18.2%). The regression models based on forward selection could effectively predict the values of Im (R2 = 0.802, RMSE = 0.049) and I% (R2 = 0.546, RMSE = 1.434). Topographic factors (altitude, slope degree and aspect) indirectly influenced both Im and I% by modulating vegetation characteristics (AGB, Cov, etc.). All these indicated that aboveground biomass mainly determines grassland community rainfall interception loss in the semiarid Loess Plateau.

&lt;i&gt;In Vitro&lt;/i&gt; Introduction of &lt;i&gt;Lespedeza davurica&lt;/i&gt; (Fabaceae)

Abstract—Rare species Lespedeza davurica (Laxm.) Schindl. (Fabaceae), growing in the Russian Federation, was for the first time introduced into in vitro culture. Efficient sterilization protocol was selected: seeds were soaked in sulfuric acid for 25 min, then washed in distilled water 5 times for 30 s, then soaked in 1% silver nitrate solution for 25 min, then in 1% sodium chloride solution for 15 min, and washed in distilled water 3 times for 30 s. The overall seed germination was sufficiently high – 78.8%. It was observed, that cotyledon leaves in most plants appeared by the end of the first week of cultivation, true leaves – by the end of the second week, additional shoots began to form within the first month of cultivation. The resulting culture was propagated under in vitro conditions using additional shoots. The effect of thidiazuron at concentrations of 0.5 and 0.1 mL/L was traced. It was shown that Murashige and Skoog medium without growth regulators are suitable for cultivation and micropropagation of the species under study, and when the medium is supplemented with thidiazuron it can be used to obtain more plant material. The results of our study are of interest for the fundamental and applied aspects of the study of L. davurica.

Drought Eliminates the Difference in Root Trait Plasticity and Mycorrhizal Responsiveness of Two Semiarid Grassland Species with Contrasting Root System.

Root traits and arbuscular mycorrhizal (AM) fungi are important in determining the access of plants to soil resources. However, whether plants with different root systems (i.e., taproot vs. fibrous-root) exhibit different root trait plasticity and mycorrhizal responsiveness under drought remains largely unexplored. Tap-rooted Lespedeza davurica and fibrous-rooted Stipa bungeana were grown in monocultures in sterilized and live soils, followed by a drought treatment. Biomass, root traits, root colonization by AM fungi, and nutrient availability were evaluated. Drought decreased biomass and root diameter but increased the root:shoot ratio (RSR), specific root length (SRL), soil NO3--N, and available P for the two species. Under control and drought conditions, soil sterilization significantly increased the RSR, SRL, and soil NO3--N for L. davurica, but this only occurs under drought condition for S. bungeana. Soil sterilization significantly reduced AM fungal root colonization of both species, but drought significantly increased it in live soil. In water-abundant conditions, tap-rooted L. davurica may depend more on AM fungi than fibrous-rooted S. bungeana; however, under drought conditions, AM fungi are of equal importance in favoring both plant species to forage soil resources. These findings provide new insights for understanding the resource utilization strategies under climate change.

Combined addition of plant litter altered remediating effects on petroleum‐contaminated soil in Northern Shaanxi, China

AbstractIn the present study, we assessed whether the nonadditive effects of mixed litter decomposition on soil biological and chemical properties, which was usually recognized in clean soils, could be used to enhance the efficiency of petroleum‐contaminated soil necrophytoremediation. In particular, six common plant species from the petroleum production region of Northern Shaanxi, China were collected, forming nine mixture types. The single and mixed litters were used to treat petroleum‐contaminated soil with a proportion of 45 g kg−1 at 25°C and a constant humidity for 150 days. The possible nonadditive effects on the efficiency of removing contaminants and recovering the damaged soil traits caused by the mixed litter addition were then investigated. The results indicate that monospecific litter treatments significantly increased the degradation rates of petroleum contaminants, the available N and P contents, and the catalase and dehydrogenase activities by 36%–74%, 28%–455%, and 8%–102%, respectively (p &lt; 0.05). The mixed addition of the litters from Lespedeza davurica and Artemisia scoparia or those from Agropyron cristatum and Bromus inermis caused significant synergistic effects, enhancing the overall petroleum component removal, replenishing nutrients (particularly nitrogen) or stimulating enzymatic activities (especially for sucrase, phosphatase, catalase, and urease). The observed values of the corresponding indicators following mixed litter treatment were observed to significantly increase by 12%–18%, 23%–58%, and 9%–24% (p &lt; 0.05), relative to their predicted values, which were calculated based on the observed values from the monospecific litter treatments and the proportion of the litter in the mixture. However, other litter combinations may weaken the remediation effects of the litter addition. In general, a high content of nutrients, primary metabolites (e.g., soluble sugars and amino acids), and the potential bio‐surfactants and co‐metabolized substrates (including terpenoids and flavonoids) of mixed litters enhanced the remediation efficiency of mixed litters. Notably, an increase in the chemical diversity of mixed litter may weaken its synergistic effects on the degradation of petroleum components and the simulation of soil polyphenol oxidase activity. Our results demonstrate that appropriate litter mixing combinations can effectively enhance the efficiency of necrophytoremediation, thus providing new approaches for the more convenient and economical remediation of petroleum‐contaminated soil.

Interactions of soil nutrients and microbial communities during root decomposition of gramineous and leguminous forages

AbstractSoil microorganisms are involved in the litter decomposition process and are closely related to nutrient cycling in ecosystems, especially carbon (C) and nitrogen (N) cycling. For grassland ecosystems, most grassland biomass is invested in the root system. Therefore, to determine the influence of root decomposition on soil microorganisms in different grassland species, an in‐situ root decomposition experiment was conducted with two species (gramineous forage: Bothriochloa ischaemum and leguminous forage: Lespedeza davurica) over three decomposition times (90, 270 and 450 days). Total organic carbon (TOC) and total nitrogen (TN) in the roots of the two species decreased gradually. And L. davurica had higher soil organic carbon (SOC) and soil total nitrogen (STN) in the late stage. Proteobacteria, Chloroflexi and Acidobacteria were the dominant bacteria, and Ascomycota and Basidiomycota were the dominant fungi in the two species. STN is the most important factor driving changes in soil microbial communities. The alpha diversity index of bacteria in both species showed an increasing trend, while in fungi, it decreased rapidly at the early stage and increased slightly at the late stage. Compared with the bacteria in B. ischaemum, L. davurica increased some submetabolic system pathway genes related to carbon cycle metabolism. FUNGuild revealed that saprotrophic fungi on the 90th day were significantly lower than those on the 270th and 450th days. Our results show that leguminous forages have better performance in improving SOC and STN, and microbial characteristics are also affected by species during root decomposition.

Enhanced soil water recovery and crop yield following conversion of 9-year-old leguminous pastures into croplands

Pasture-crop rotation has been considered as an efficient agronomical practice to improve soil and water conservation, develop livestock production, and promote food security. However, the characteristics of soil water restoration and performances of crop yield and water use efficiency (WUE) after conversion of long-term leguminous pasture into croplands still remain unclear. A field experiment was conducted in China’s Loess Plateau to investigate soil water restoration and wheat yields in crop rotation with Italian ryegrass (Festuca perennis Lam.) and winter wheat (Triticum aestivum L.) converted from three 9-year-old leguminous pastures, viz. milk vetch (Astragalus adsurgens Pall.), alfalfa (Medicago sativa L.) and bush clover (Lespedeza davurica S.), and unplanted control (fallow). Soil water in the alfalfa treatment gradually recovered from up to down compared to the fallow treatment (control) during cultivation phase. After one year of rotation, the recovery levels of soil water in the three pasture-crop rotation systems at 0–500 cm soil depth were 97.1%, 95.5% and 94.2%, respectively, compared to the fallow treatment. The legume treatments significantly enhanced the crop yield (35.6%−64.5%), aboveground biomass (28.7%−59.4%) and WUE (60%−68.3%) of winter wheat compared with fallow. These results imply that the concerns about soil desiccation from long-term alfalfa was resolvable after long-term alfalfa converted into cropland in the rainfed farming area of Loess Plateau. The results also suggest that legume pasture-crop rotation can facilitate achieving a sustainable development of rainfed farming.

Implications of plant N/P stoichiometry influenced by arbuscular mycorrhizal fungi for stability of plant species and community in response to nutrient limitation

Arbuscular mycorrhizal fungi (AMF) influence plant nitrogen/phosphorus (N/P) by modifying plant N and P uptake, which further affects plant stoichiometric N/P homeostasis. Plant species and community stoichiometric N/P homeostasis can impact plant species and community stability, respectively, in response to variations of soil N and P availabilities. We investigated interspecific plant interactions via AMF in regard to plant and soil microbial N/P stoichiometry across different soil N and P availabilities induced by N and P addition (0 mg N kg−1, 25 mg N kg−1, 50 mg N kg−1, 30 mg P kg−1 and 100 mg P kg−1). We selected one dominant (Bothriochloa ischaemum; C4 grass) and one subordinate (Lespedeza davurica; legume) species in a natural grassland climax community. We examined how AMF influences stoichiometric N/P homeostasis in monoculture and mixed culture systems, and the resulting consequences for temporal stability of plant species and community in response to variations in soil N and P availability.The AMF mitigated the P limitation of soil microbial communities and decreased the degree of stoichiometric N/P homeostasis of host plants in monoculture. Through their resource‐scavenging and soil organic matter mineralisation functions, AMF enhances plant ‘luxury consumption', promoting species stability in monoculture in response to soil N and P availability variations. Compared with plants in monoculture, the interaction between B. ischaemum and L. davurica via AMF increased shoot N/P under soil N‐poor conditions, leading to an enhanced degree of stoichiometric N/P homeostasis in both plant species, especially the legume.Our results suggest that interspecific plant interaction between C4 grass and legume mediated by AMF confers an advantage in complementarity in plant N acquisition under N‐poor conditions, leading to increased stability of plant communities and better maintenance of subordinate species (legume) in response to soil N deficiency.

Clipping decreases plant cover, litter mass, and water infiltration rate in soil across six plant community sites in a semiarid grassland

Water infiltration in the soil is a crucial hydrological function in the land water cycle, especially in the semiarid region where water is relatively scarce. The semiarid grassland in Northern China represents the regional vegetation in the vast area of Eurasian continent and is sensitive to land use change. However, no clear patterns exist regarding the comprehensive examination of water infiltration in relation to clipping across six plant community sites. This study aimed to test the effect of clipping and plant community sites, which were dominated by Agropyron cristatum, Stipa krylovii, Leymus chinensis, Potentilla tanacetifolia, Artemisia frigida, or Lespedeza davurica, on the water infiltration rate in the semiarid grassland. Clipping significantly decreased the water initial, steady, and average infiltration rates by 39.13, 4.36, and 12.46 mm h−1, respectively, across the six plant community sites. Clipping-induced changes in the average infiltration rate positively correlated with the changes in the plant cover (r = 0.60, P < 0.01), litter mass (r = 0.53, P < 0.01), forb functional group ratio (r = 0.46, P = 0.03), and total porosity (r = 0.49, P = 0.02), and negatively with water-holding capacity (r = −0.45, P = 0.03). Further, the water infiltration rate significantly differed among the six plant community sites. The L.davurica site had the highest water initial infiltration rate with a value of 137.63 ± 17.76 mm h−1, while the L. chinensis site had the lowest rate with a value of 74.08 ± 5.26 mm h−1. Principal component analysis showed that the total porosity, litter mass, plant cover, and forb functional group ratio were the main factors affecting water infiltration rates in the control grassland. Overall, our findings suggested that local governments and herders should implement unclipping as a potential sustainable management for improving hydrological function in the semiarid grassland.

Leaf Photosynthetic and Functional Traits of Grassland Dominant Species in Response to Nutrient Addition on the Chinese Loess Plateau

Leaf photosynthetic and functional traits of dominant species are important for understanding grassland community dynamics under imbalanced nitrogen (N) and phosphorus (P) inputs. Here, the effects of N (N0, N50, and N100, corresponding to 0, 50, and 100 kg ha-1 yr-1, respectively) or/and P additions (P0, P40, and P80, corresponding to 0, 40, and 80 kg ha-1 yr-1) on photosynthetic characteristics and leaf economic traits of three dominant species (two grasses: Bothriochloa ischaemum and Stipa bungeana; a leguminous subshrub: Lespedeza davurica) were investigated in a semiarid grassland community on the Loess Plateau of China. Results showed that, after a three-year N addition, all three species had higher specific leaf area (SLA), leaf chlorophyll content (SPAD value), maximum net photosynthetic rate (PNmax), and leaf instantaneous water use efficiency (WUE), while also having a lower leaf dry matter content (LDMC). The two grasses, B. ischaemum and S. bungeana, showed greater increases in PNmax and SLA than the subshrub L. davurica. P addition alone had no noticeable effect on the PNmax of the two grasses while it significantly increased the PNmax of L. davurica. There was an evident synergetic effect of the addition of N and P combined on photosynthetic traits and most leaf economic traits in the three species. All species had relatively high PNmax and SLA under the addition of N50 combined with P40. Overall, this study suggests that N and P addition shifted leaf economic traits towards a greater light harvesting ability and, thus, elevated photosynthesis in the three dominant species of a semiarid grassland community, and this was achieved by species-specific responses in leaf functional traits. These results may provide insights into grassland restoration and the assessment of community development in the context of atmospheric N deposition and intensive agricultural fertilization.

The contribution of understory and Compositae species to canopy storage capacity of semiarid grassland communities on the Loess Plateau

AbstractCanopy rainfall interception reduces the effectiveness of limited rainfall resources in arid and semiarid regions. To clarify the effects of species composition and community vertical structure on canopy storage capacity, the artificial wetting and simulated rainfall methods were used to determine the species (C) and community (Cmax) water storage, respectively, in three typical grassland communities on the semiarid Loess Plateau. Results indicated that water storage capacity of 31 grassland species ranged from 0.47 to 3.73 g g−1, with an average of 1.60 g g−1, and leaf storage capacity was significantly higher than the stem. Plant storage capacity was correlated with leaf traits (including leaf fresh weight, length and area). Canopy storage capacity of three grassland communities (Bothriochloa ischaemum, Artemisia gmelinii and Lespedeza davurica) ranged from 0.77 to 1.09 mm and were positively correlated with community leaf area index (LAI), coverage and leaf dry biomass. Leaf and stem water storage accounted for 57.6% and 42.4% of the total community, respectively. The water storage of Compositae, Gramineae, Leguminosae and other species accounted for 35.5%, 27.0%, 23.4% and 14.1%, respectively. The plants in the community with heights of &gt;40, 20–40 and 0–20 cm contributed 5.8%, 30.3% and 63.9% of the water storage, respectively. The field observed canopy storage capacity was significantly higher than the estimated value through scaling up the individual storage data to the community, revealing complex community structure and species composition may increase actual rainfall interception. These results highlighted the species at 0–20 cm height was the key component affecting canopy water storage, and Compositae species may intercept more rainfall within the community, which imply that reducing the understory or Compositae species composition of grassland community would be helpful for increasing limited rainfall partitioning to soil in the drought area.

Biomass Allocation and Competitive Ability of a Semiarid Perennial Grass and a Legume in Mixtures under Periodical Soil Water Decreasing Conditions

Soil moisture is the key factor controlling plant growth in semiarid grasslands. Here, we sought to evaluate the effects of soil moisture decreasing at different growth stages on biomass accumulation, water use efficiency, and plant-plant interaction of a C3 leguminous subshrub Lespedeza davurica (L) and a C4 perennial grass Bothriochloa ischaemum (B) when sown singly and as a mix in five different ratios in a pot experiment. Results showed that soil water decrease significantly reduced total biomass production of the mixtures by 3.7–53.8% compared with well-watered conditions, and plants at the heading and flowering periods were more vulnerable to soil water decline than those at the late stage. The relative yield total (RYT) of the mixtures was mostly greater than those sown singly. Soil water decreasing increased root/shoot ratio and water use efficiency (WUE) of the mixtures, and such effects were mediated by mixture ratio and/or growth stage. In the mixtures, a strong intraspecific competition was observed in B. ischaemum, whereas interspecific competition in L. davurica. The highest overall biomass (86.47 g pot−1) and WUE (6.33 g kg−1) were observed when the mixture ratio was B:L = 10:2 regardless of soil moisture, and thus could be considered an optimal mixture ratio for establishing restored grassland using the two species. Our results suggest that sown seed mixtures of the two species with an appropriate ratio could sustain a relatively high total biomass production and improve WUE under soil water decreasing conditions in the semiarid Loess Plateau.

Effects of Drought on the Growth of Lespedeza davurica through the Alteration of Soil Microbial Communities and Nutrient Availability.

Lespedeza davurica (Laxm.) is highly important for reducing soil erosion and maintaining the distinctive natural scenery of semiarid grasslands in northwest China. In this study, a pot experiment was conducted to investigate the effects of drought (20% water-holding capacity) on biomass and its allocation, root characteristics, plant hormones, and soil microbial communities and nutrients after L. davurica was grown in a greenhouse. Drought reduced the total biomass of L. davurica but increased the root:shoot biomass ratio. In addition, drought altered the composition and structure of microbial communities by limiting the mobility of nutrients in non-rhizosphere soils. In particular, drought increased the relative abundances of Basidiomycota, Acidobacteria, Actinobacteria, Coprinellus, Humicola and Rubrobacter, which were closely positively related to the soil organic carbon, pH, available phosphorus, ammonia nitrogen (N) and nitrate N under drought conditions. Furthermore, soil fungi could play a more potentially significant role than that of bacteria in the response of L. davurica to drought. Consequently, our study uncovered the effects of drought on the growth of L. davurica by altering soil microbial communities and/or soil nutrients, thus providing new insights for forage production and natural grassland restoration on the Loess Plateau of China.

Leaf Physiological Responses of Three Psammophytes to Combined Effects of Warming and Precipitation Reduction in Horqin Sandy Land, Northeast China.

The decreasing precipitation with global climate warming is the main climatic condition in some sandy grassland ecosystems. The understanding of physiological responses of psammophytes in relation to warming and precipitation is a possible way to estimate the response of plant community stability to climate change. We selected Lespedeza davurica, Artemisia scoparia, and Cleistogenes squarrosa in sandy grassland to examine the effect of a combination of climate warming and decreasing precipitation on relative water content (RWC), chlorophyll, proline, and antioxidant enzyme activities. We found that all experimental treatments have influenced RWC, chlorophyll, proline, and antioxidant enzyme activities of three psammophytes. L. davurica has the highest leaf RWC among the three psammophytes. With the intensification of precipitation reduction, the decreasing amplitude of chlorophyll from three psammophytes was L. davurica > C. squarrosa > A. scoparia. At the natural temperature, the malondialdehyde (MDA) content of the three psammophytes under severe drought treatment was much higher than other treatments, and their increasing degree was as follows: A. scoparia > C. squarrosa > L. davurica. At the same precipitation gradient, the proline of three psammophytes under warming was higher than the natural temperature. The differences in superoxide dismutase (SOD) among the three psammophytes were A. scoparia > L. davurica > C. squarrosa. Moreover, at natural temperature, more than 40% of precipitation reduction was most significant. Regardless of warming or not, the catalase (CAT) activity of A. scoparia under reduced precipitation treatments was higher than natural temperature, while the response of L. davurica was opposite. Correlation analyses evidenced that warming (T) was significant in L. davurica and precipitation (W) was significant in A. scoparia and C. squarrosa according to the Monte-Carlo permutation test (p = 0.002, 0.004, and 0.004). The study is important in predicting how local plants will respond to future climate change and assessing the possible effects of climate change on sandy grassland ecosystems.

Seed production and yield components of Lespedeza davurica in response to N, P, and K fertilization and plant density

Lespedeza davurica Laxm is a valuable forage because of the strong cold and drought tolerance, and its high nutritional value. This crop production is limited by seed supply. The objective of this study was to investigate the effects of fertilization and plant density on seed yield. “JinNong 1” was drill-seeded in 2016 at 15 kg ha−1 at the Forage Research Station of Shanxi Agricultural University. The seedlings were manually thinned in May 2016 to two different densities, 6 and 12 plants m−2 in the main plots. Within each main plot, a factorial combination of N, P, and K fertilization levels were applied once a year from 2016 to 2018. The N levels were 0, 75, 125, and 175 kg ha−1. The P levels were 22 and 44 kg ha−1. The K levels were 62 and 124 kg ha−1. Maximum seed yield was achieved at the density of 12 plants m−2, 75 kg ha−1 of N, 22 kg ha−1 of P, and 124 kg ha−1 of K. The seed yields were 750 and 644 kg ha−1 during 2017 and 2018, respectively. High plant density showed a tradeoff with the number of primary and secondary branches, the number of raceme per branch, and 1000-seed weight. The number of pods per raceme and the number of flowers per raceme did not show a tradeoff at high density. Therefore, selecting for higher numbers of seed pods per raceme or fertile flowers may be a practical objective for breeders attempting to increase seed production.

Soil Water Availability Changes in Amount and Timing Favor the Growth and Competitiveness of Grass Than a Co-dominant Legume in Their Mixtures.

The grasslands on the semi-arid Loess Plateau of China are expected to be particularly responsive to the size and frequency changes of extreme precipitation events because their ecological processes are largely driven by distinct soil moisture pulses. However, the plant growth and competitiveness of co-dominant species in response to the changes in the amount and timing of soil water are still unclear. Thus, two co-dominant species, Bothriochloa ischaemum and Lespedeza davurica, were grown in seven mixture ratios under three watering regimes [80 ± 5% pot soil capacity (FC) (high watering), 60 ± 5% FC (moderate watering), and 40 ± 5% FC (low watering)] in a pot experiment. The soil water contents were rapidly improved from low to moderate water and from moderate to high water, respectively, at the heading, flowering, and maturity stages of B. ischaemum, and were maintained until the end of the growing season of each species. The biomass production of both species increased significantly with the increased soil water contents, particularly at the heading and flowering periods, with a more pronounced increase in B. ischaemum in the mixtures. The root/shoot ratio of both species was decreased when the soil water availability increased at the heading or flowering periods. The total biomass production, water use efficiency (WUE), and relative yield total (RYT) increased gradually with the increase of B. ischaemum in the mixtures. The relative competition intensity was below zero in B. ischaemum, and above zero in L. davurica. The competitive balance index calculated for B. ischaemum was increased with the increase of the soil water contents. Bothriochloa ischaemum responded more positively to the periodical increase in soil water availability than L. davurica, indicating that the abundance of B. ischaemum could increase in relatively wet seasons or plenty-rainfall periods. In addition, the mixture ratio of 10:2 (B. ischaemum to L. davurica) was the most compatible combination for the improved biomass production, WUE, and RYTs across all soil water treatments.

Mechanistic understanding of interspecific interaction between a C4 grass and a C3 legume via arbuscular mycorrhizal fungi, as influenced by soil phosphorus availability using a 13 C and 15 N dual-labelled organic patch.

Arbuscular mycorrhizal fungi (AMF) can improve plant nutrient acquisition, either by directly supplying nutrients to plants or by promoting soil organic matter mineralization, thereby affecting interspecific plant relationships in natural communities. We examined the mechanism by which the addition of P affects interspecific interactions between a C4 grass (Bothriochloa ischaemum, a dominant species in natural grasslands) and a C3 legume (Lespedeza davurica, a subordinate species in natural grasslands) via AMF and plant growth, by continuous 13 C and 15 N labelling, combined with soil enzyme analyses. The results of 15 N labelling revealed that P addition affected the shoot uptake of N via AMF by B.ischaemum and L.davurica differently. Specifically, the addition of P significantly increased the shoot uptake of N via AMF by B.ischaemum but significantly decreased that by L.davurica. Interspecific plant interactions via AMF significantly facilitated the plant N uptake via AMF by B.ischaemum but significantly inhibited that by L.davurica under P-limited soil conditions, whereas the opposite effect was observed in the case of excess P. This was consistent with the impact of interspecific plant interaction via AMF on arbuscular mycorrhizal (AM) benefit for plant growth. Our data indicate that the capability of plant N uptake via AMF is an important mechanism that influences interspecific relationships between C4 grasses and C3 legumes. Moreover, the effect of AMF on the activities of the soil enzymes responsible for N and P mineralization substantially contributed to the consequence of interspecific plant interaction via AMF for plant growth.

N enrichment affects the arbuscular mycorrhizal fungi-mediated relationship between a C4 grass and a legume.

Arbuscular mycorrhizal fungi (AMF) regulate soil nutrient cycling, directly supplying a host plant with nitrogen (N). AMF can also affect the outcome of interspecific interactions, but a mechanistic understanding of how soil N availability affects AMF-mediated interspecific relationships is currently lacking. We selected one dominant (Bothriochloa ischaemum; C4 grass) and one subordinate (Lespedeza davurica; legume) species in a natural grassland climax community to investigate the mechanism by which AMF influence interspecific interaction (mixed and monoculture) under three levels of N addition (0, low, and high N addition). Under the non-N addition treatment, AMF preferentially supplied N to the roots of B. ischaemum at the expense of N uptake by L. davurica, resulting in inhibited AMF benefits for L. davurica shoot growth. Under the low N addition treatment, interspecific interaction via AMF promoted L. davurica growth. Compared to the non-N addition treatment, N addition largely mitigated the effects, both positive (for B. ischaemum) and negative (for L. davurica), of AMF-mediated interspecific interaction on plant N uptake via AMF. When soil N availability severely limited plant growth, preferential N supply to the C4 grass by AMF was important for maintaining the abundance of the dominant species. When the N limitation for plant growth was alleviated by N addition, the interaction between AMF and soil microorganisms improved nutrient availability for the legume by stimulating activity of the enzyme responsible for soil organic matter mineralization, which is important for maintaining the abundance of the subordinate species. These data could influence strategies for maintaining biodiversity.

Responses of soil respiration to rainfall depth and frequency in semiarid grassland communities

AbstractClimate change is increasing the extreme precipitation depth and frequency, which may cause a strong response of ecological processes in drought regions. To investigate how rainfall depth and frequency alter soil respiration (SR), a rainfall simulation experiment was conducted in grassland communities dominated by Artemisia gmelinii and Lespedeza davurica in Loess Plateau of China. SR rate (Rs), soil temperature (Ts) and soil volumetric water content (Sv) were monitored before and after the rainfall treatments, that is, four depths (5, 10, 20 and 40 mm) and three frequencies (40 mm × 1, 20 mm × 2 and 10 mm × 4) during the growing season (June to September). Results indicated that the response magnitude of Rs increased with rainfall depths, reaching the maximum under 40 mm, and the increments were tightly related to rainfall frequency and community type. The increase and mean value of Rs in A. gmelinii community were significantly higher than those in L. davurica and bare land under same rainfall depth. L. davurica community was more sensitive to rainfall lower than 10 mm, whereas it had weaker but longer response under rainfall larger than 10 mm compared with A. gmelinii community. Successive rainfall events dampened the pulse effect of Rs but generated more cumulative CO2 emission in vegetation communities. Ts and Sv varied significantly with rainfall depth and co‐regulated SR. These findings implied more CO2 will be released from soil in the semiarid grasslands under extreme and successive rainfalls and emphasized the importance of species impact on SR for soil carbon evaluation under future rainfall regimes.