1. Plants are often exposed to multiple abiotic and biotic environmental variations in nature, but studies are very scarce on how plant respond to biotic variations, or interactive effects of abiotic and biotic factors. 2. Our objective was to investigate effects of light conditions on responses of plant biomass allocation to conspecific or heterospecific neighbors, and effects of these neighbors on plant response to shading vs. full light conditions. 3. We subjected plants of Buddleja lindleyana and Bidens pilosa to three treatments of solitary growth (control), intra- and interspecific interaction, under 50% shading and full light conditions, and measured a series of biomass and morphological traits on them. 4. Full light relative to shading decreased total mass, root mass and root:shoot ratio of B. pilosa under intraspecific competition, but increased them for both species grown alone and with heterospecific neighbors. Compared to those grown alone, intraspecific interaction increased mean total mass for B. lindleyana and increased root mass and root: shoot ratio for both species in shading, but reduced total mass and root:shoot ratio of B. pilosa under full light, with no effects of interspecific interaction. 5. Results suggested conspecific neighbors will more likely interfere with plant acquiring resources, making it more difficult or less efficient for plants to utilize the resources. Plants will adjust the strategy of biomass allocation for maximizing growth depending on both resource availability and accessibility, to enhance the efficiency of resource acquiring under severe environmental challenges. 6. Synthesis. By investigating responses of plants to variations in abiotic conditions and plant interactions simultaneously, we not only provided direct evidence for responses of plants to complex environmental factors, but also revised the optimal partitioning theory by emphasizing the importance of resource accessibility.

The relationships among developmental stability, canalization and phenotypic plasticity are not straightforward, but may be better understood in the context of temporally heterogeneous environments. Our objective was to investigate the effects of early experience with temporally heterogeneous water availability on the associations between developmental stability, canalization and phenotypic plasticity. We subjected eight plant species to a first round of alternating inundation and drought vs. constantly moderate water treatments and a second round of water conditions. Fluctuating asymmetry (FA), intra- and inter-individual variation (CVintra and CVinter), and plasticity in traits were measured and correlations between variables were calculated for each species. Early temporally heterogeneous experience decreased the leaf size of half of the species, but had complex effects on leaf fluctuating asymmetry (FA) and inter-individual variation (CVinter) in traits immediately or in late conditions, with little effects on intra-individual variation (CVintra). There were several positive correlations between FA and CVinter, positive correlations between CVinter and plasticity in early treatments, but negative correlations in late treatments. Our results suggested complexity and variability in the relationships between different mechanisms. Decreased canalization may promote plastic responses in traits before or during the induction of plasticity, whereas canalization may reflect phenotypic convergence after plastic responses. Temporally heterogeneous experiences may facilitate positive correlations or attenuate negative correlations between decreased canalization and plasticity. We provide direct evidence for relationships between developmental stability, canalization and plasticity as well as the role of temporally heterogeneous environments in modifying these processes. The integrative way that plants deal with environmental variation demonstrates their ability to evolve in multiple directions via many flexible adjustments in response to varying environmental signals over a plant’s lifetime.

METHODS A field experiment was conducted by subjecting plants of Abutilon theophrasti to four periods of emergence in spring (ET1), late spring (ET2), summer (ET3) and late summer (ET4), and measuring a number of traits, to calculate and analyze the correlations of plasticity with canalization and integration in these traits at two growth stages. RESULTS Plants with delayed emergence had higher level of phenotypic integration, but only the plants emerged in late spring (ET2) had a case of negative correlation between integration and plasticity; decreased canalization had more positive correlations with plasticity in plants except for those emerged in summer (ET3). CONCLUSIONS Our results suggest that the relationships of plasticity with integration and canalization in traits will more rely on induced plasticity in traits is active or not and its strength, rather than the nature of environments. Plants have the intelligence to regulate individual-level mechanisms such as phenotypic integration and its relationship with plasticity to deal with within-generation challenges, but regulate population-level mechanisms such as canalization combined with plasticity in face of future-generations challenges