Potential changes in phytoplankton community structure in shallow lakes due to land use could pose a serious threat to ecosystem sustainability and functioning. Nevertheless, this effect has not been analyzed in detail. In this study, we chose two adjacent lakes, the main land use types around them are farmland and forest, respectively. We investigated the spatial differences in the phytoplankton community structure, water quality physicochemical parameters, and land use patterns in the two lakes. The results indicated that the annual average cell density and biomass of phytoplankton in the former were 1.84 times and 2.38 times that of the latter, respectively. The results of Pearson correlation and Redundancy analysis showed that total nitrogen (TN), total phosphorus (TP), water depth (WD), and water temperature (WT) were the main environmental factors influencing the structural changes of phytoplankton communities in the two lakes. The results indicated that different land use patterns, such as farmland and towns around the lake, increase the nitrogen (N) and phosphorus (P) content of the lake, while the forests distributed around the lake can reduce the N and P entering the lake, which is probably the main reason for the spatial difference in the characteristics of phytoplankton communities in the two lakes. Our results highlight that land use significantly affects the community structure of phytoplankton by influencing physicochemical factors in water bodies. Our study can provide guidance for pollution control and water quality management of shallow lakes.

Aims: Plant investment in sexual reproduction is affected by nitrogen (N): phosphorus (P) stoichiometry. It has been suggested that an important adaptation to strong P limitation is reduced investment in sexual reproduction. We aim to investigate the specific influence of N:P on sexual reproduction performance within and between grassland species. Methods: Eleven grassland species were selected in ten plots covering N limitation, co-limitation and P limitation. Nutrients in soil and above-ground biomass were determined, plus soil pH and soil moisture. A range of sexual reproduction traits were measured as a proxy for investment in sexual reproduction. Results: At the intraspecific level: compared with N-limited plots, in P-limited/co-limited plots, flowering time was later, flowering period in individuals was shorter, and number of flowers (inflorescences) per individual was smaller. At the interspecific level, in P-limited/co-limited plots, species had a significantly earlier flowering time and a longer seed stalk and seed panicle, than those in N-limited plots. However, flowering period was shorter and number of flowers (inflorescences) per individual was smaller under P limitation/co-limitation. Moreover, significant correlations between soil pH and soil moisture, and sexual reproduction performance of the selected grassland species were also found. Conclusions: P limitation/co-limitation restrict the sexual reproduction of grassland species, which may hamper their dispersal capacity. We recommend future studies further analyze the relationship between soil pH and N:P stoichiometry and the influence of soil pH, as well as soil moisture on sexual reproduction performance of grassland species in addition to analyzing N:P stoichiometry.

Mineral nutrients influence photosynthesis and tissue formation; a shift from nitrogen (N)-limited to phosphorus (P)-limited growth induced by high N deposition may change plant growth in terms of physiology and morphology. This experiment showed that absolute and relative N and P supply affected net photosynthesis (source activity) and biomass formation (sink activity), and the relationship between source and sink activities of Holcus lanatus L. under various nutrient treatments. H. lanatus was grown at three N:P ratios (5, 15, 45) with two absolute supply levels of N and P. Between N:P 5 at low level and N:P 45 at high level, and between N:P 45 at low level and N:P 5 at high level, there was a nine-fold difference in N and P supply. Maximum light-saturated net photosynthesis rate (Amax), specific leaf area (SLA), leaf area, and shoot and root biomass were determined during and after the growth process. Amax was minimal at N:P 5 and increased only with increasing absolute N supply. Neither SLA nor leaf area were affected by N:P; increasing absolute P supply significantly increased leaf area. Shoot and root biomass were minimal at N:P 45 and increased dramatically with increasing absolute P supply. Plant biomass was not correlated with Amax. Our results highlight that H. lanatus growth is predominantly controlled by P supply and to a lesser extent by N, whereas net photosynthesis exerted no apparent control on growth under these sink-limited growth conditions. Our findings contribute to understanding of plant growth under sink-limited conditions.

Nitrogen (N) and phosphorus (P) availability affect plant sexual reproduction performance. Seed as the main product of sexual reproduction is expected to be affected by N and P availability in parent plant. We experimentally test how parental N:P stoichiometry affected seed characteristics and performance of two grassland species. Seeds of a common species (Holcus lanatus) and an endangered species (Parnassia palustris) were collected from parent plants under two different N:P ratio growth conditions in a grassland reserve in the Netherlands. We measured the following traits of the two species from the two parental N:P ratio growth conditions: seed N concentration and content, seed P concentration and content, seed length, seed area, seed weight, seed germination, and offspring survival. No significant inter-location difference was found in seed weight of the collected seeds for either of the two species. However, the stronger P-limited conditions at the locations of the parent plants affected seed length and seed area negatively in H. lanatus and positively in P. palustris. Stronger P-limited conditions also decreased seed P concentration and content and increased seed N:P ratio of H. lanatus, but no inter-location nutrient difference was found in seeds of P. palustris. Surprisingly, contrary to what could be expected from seed P concentration and content there was no inter-location difference in seed germination for H. lanatus. For P. palustris, stronger P-limited conditions in the parental environment significantly enhanced seed germination, whereas stronger P-limited conditions in the offspring environment decreased offspring survival, suggesting that P limitation may negatively affect P. palustris rejuvenation. Our results suggest the possibility of different influences of parental N:P ratio and especially of P limitation on seed characteristics and performance of a common and an endangered species.