Competition for water probably makes plants more sensitive to the water heterogeneity. In addition, the intensity of intraspecific competition can be affected by the temporal patterns of water supply. Because both resource heterogeneity and intraspecific competition affect resource acquisition and growth of plants, their interactive effects should be evaluated more carefully under future studies.

Temporal heterogeneity of water supply can alter the biomass growth of plants, even when the same total amount of water is provided. Most studies of heterogeneous watering have focused on responses of whole populations rather than individuals in a population. The effects of water supply heterogeneity may also depend on nutrient levels. Thus, we investigated the integrated effects of water supply heterogeneity and nutrient levels on plants within a population. Six plants of Perilla frutescens per pot were grown under different combinations of frequency of water supply and nutrient level. The effects on yield per pot, individual biomass, and allocation to roots were analyzed after a 44‐day watering regime. A homogeneous water supply resulted in a greater yield per pot and greater biomass of individual plants than a heterogeneous supply. However, the interaction between water supply heterogeneity and nutrient level was significant only in larger individuals, not in smaller plants or at the p. Water supply heterogeneity affected the growth of all plants, but the effects differed among individuals depending on their relative size within their population. It is therefore important to focus not only on whole‐population characteristics such as yield but also on individuals in a population in order to reveal the detailed effects of water supply heterogeneity.

Temporal heterogeneity of watering affects plant growth. When the same total amount of water is supplied, frequent watering leads to greater plant size than infrequent watering. However, the effects of a given watering regime can differ when nutrient levels vary. An experiment was designed to test the hypothesis that the effects of temporal heterogeneity of watering on plant growth also vary as a function of nutrient levels. Perilla frutescens (L.) Britton was grown using different combinations of nutrient levels and watering frequencies, with total water held constant across the treatments. The effects on plant size were analysed after 36 d. Under nutrient-rich conditions, frequent watering resulted in significantly larger plants than infrequent watering. However, under nutrient-poor conditions, no significant difference was detected between the different watering frequencies. The temporal heterogeneity of watering thus appears to have different effects on plant growth at different nutrient levels. Therefore, the watering heterogeneity should be examined with nutrients as unity, because the watering heterogeneity and nutrients affect plant growth in an interactive manner.

Temporal heterogeneity of water supply affects grassland community productivity and it can interact with nutrient level and intraspecific competition. To understand community responses, the responses of individual species to water heterogeneity must be evaluated while considering the interactions of this heterogeneity with nutrient levels and population density. We compared responses of four herbaceous species grown in monocultures to various combinations of water heterogeneity, nutrient level, and population density: two grasses (Cynodon dactylon and Lolium perenne), a forb (Artemisia princeps), and a legume (Trifolium repens). Treatment effects on shoot and root biomass were analyzed. In all four species, shoot biomass was larger under homogeneous than under heterogeneous water supply. Shoot responses of L. perenne tended to be greater at high nutrient levels. Although root biomass was also larger under homogeneous water supply, effects of water heterogeneity on root biomass were not significant in the grasses. Trifolium repens showed marked root responses, particularly at high population density. Although greater shoot and root growth under homogeneous water supply appears to be a general trend among herbaceous species, our results suggested differences among species could be found in the degree of response to water heterogeneity and its interactions with nutrient level and intraspecific competition.

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