The seedlings of wheat were treated by salt-stress (SS, molar ratio of NaCl: Na₂SO₄ = 1: 1) and alkali-stress (AS, molar ratio of NaHCO₃: Na₂CO₃ = 1: 1). Relative growth rate (RGR), leaf area, and water content decreased with increasing salinity, and the extents of the reduction under AS were greater than those under SS. The contents of photosynthetic pigments did not decrease under SS, but increased at low salinity. On the contrary, the contents of photosynthetic pigments decreased sharply under AS with increasing salinity. Under SS, the changes of net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were similar and all varied in a single-peak curve with increasing salinity, and they were lower than those of control only at salinity over 150 mM. Under AS, P _N, g _s, and E decreased sharply with rising salinity. The decrease of g _s might cause the obvious decreases of E and intercellular CO₂ concentration, and the increase of water use efficiency under both stresses. The Na⁺ content and Na⁺/K⁺ ratio in shoot increased and the K⁺ content in shoot decreased under both stresses, and the changing extents under AS were greater than those under SS. Thus SS and AS are two distinctive stresses with different characters; the destructive effects of AS on the growth and photosynthesis of wheat are more severe than those under SS. High pH is the key feature of the AS that is different from SS. The buffer capacity is essentially the measure of high pH action on plant. The deposition of mineral elements and the intracellular unbalance of Na⁺ and K⁺ caused by the high pH at AS might be the reason of the decrease of P _N and g _s and of the destruction of photosynthetic pigments.

Summary: 1. The ability to suppress neighbour growth and the ability to withstand growth suppression are widely viewed as two forms of competition, competitive effect and competitive response. 2. We conducted a greenhouse experiment to determine whether these two forms of competition were functionally linked, and to determine which plant traits are associated with effect and response competitive abilities among seedlings of 22 perennial North American prairie species. We further explored the trait‐function relationship by growing plants under different soil fertilities and with different neighbour species. 3. To determine competitive abilities, we used a phytometer approach with two phytometer species: Poa pratensis and Achillea millefolium grown in competition with each of the 22 focal species under low and high fertility. Root and shoot morphological traits were measured and principal component analyses were used to reduce the dimensionality of the data. Three axes were extracted, which roughly corresponded to size, root and shoot architecture. 4. The hierarchy of competitive effect ability of the target species did not vary with either soil fertility or neighbour identity, while the hierarchies of competitive response abilities were highly variable among the treatments. Competitive effect ability was closely associated with size‐related traits under high nutrient conditions, and with root‐related traits under low nutrient conditions. In contrast, few plant traits axes were related to competitive response. 5. These findings indicate significant differences between competitive effect and response ability. We suggest competitive effect ability is a consistent trait of a species, linked to specific plant traits. In contrast, we found little evidence to support the idea that competitive response ability is itself a species trait, and instead it appears this may be simply a collection of different ways of avoiding or tolerating competition and/or low nutrient conditions. Supporting this argument was a lack of any consistency in which traits were associated with competitive response ability. 6. We recognize the limitations of a single study of seedlings under greenhouse conditions. However, we suggest these findings indicate a need to critically examine current assumptions about plant competition, how it is defined, and the traits which control a species’ competitive ability.

Compost is considered to be superior fertilizer for soil quality and productivity, and is commonly used with chemical fertilizer. The optimal mixed ratio of compost with chemical fertilizer and the best application time is necessary to know for sustainable agriculture practices and management. Compared to the control treatment, this study comprehensively evaluated the effects of four mixed ratios of compost with chemical fertilizer, two nitrogen application times of chemical fertilizer, and their interaction on the soil properties, plant traits, yield, and quality of tomato plants. The soil properties, plant traits, and yield of tomato with all compost-mixed fertilizers performed better than the treatment without fertilizer. Furthermore, the amounts of available nitrogen, phosphorus, organic matter, plant weight, and yield in a 30% chemical fertilizer + 70% compost treatments (CF30) were even better than those with pure chemical fertilizer (CF100). No significant effect of nitrogen application time and its interaction with the mixed ratio treatment was detected, and the quality of fruit remained consistent among treatments. This study demonstrated a suitable practical application method for cow manure compost as a nutrient source in tomato crop production under silty loam soil.