Increased planting densities have boosted maize yields. Upright plant architecture facilitates dense planting. Here, we cloned UPA1 (Upright Plant Architecture1) and UPA2, two quantitative trait loci conferring upright plant architecture. UPA2 is controlled by a two-base sequence polymorphism regulating the expression of a B3-domain transcription factor (ZmRAVL1) located 9.5 kilobases downstream. UPA2 exhibits differential binding by DRL1 (DROOPING LEAF1), and DRL1 physically interacts with LG1 (LIGULELESS1) and represses LG1 activation of ZmRAVL1. ZmRAVL1 regulates brd1 (brassinosteroid C-6 oxidase1), which underlies UPA1, altering endogenous brassinosteroid content and leaf angle. The UPA2 allele that reduces leaf angle originated from teosinte, the wild ancestor of maize, and has been lost during maize domestication. Introgressing the wild UPA2 allele into modern hybrids and editing ZmRAVL1 enhance high-density maize yields.

Human activities can cause resource fluctuations through reducing uptake by the resident vegetation (e.g. disturbance) or through changing external resource supply (e.g. fertilization). Resource fluctuations often occur as pulses which are low frequency, large magnitude and short duration and now are recognized as an important driver of plant invasions. However, resource pulses often vary dramatically in a number of attributes, yet how these attributes mediate the impacts of resource pulses on plant invasions remains unclear. Erigeron canadensis is a serious invader of disturbed habitats and agricultural fields in China. Thus, it experiences nutrient pulses with different magnitudes and timings. Here, we grew E. canadensis and six co-occurring native plant species with three different magnitudes of nutrient enrichment (low, medium, or high).For each magnitude, we added equivalent amounts of nutrients with a constant supply as a control or one of three pulses with different timings (early, middle, or late stages). We found that pulse magnitude, timing and their interaction significantly affected E. canadensis growth (biomass production) and invasion (proportion of biomass in a pot). For each timing, E. candensis growth and invasion increased with nutrient magnitude. At low magnitude, middle and late pulses promoted E. canadensis growth and invasion. At medium magnitude, late pulses suppressed E. canadensis growth, but did not affect its invasion. At high magnitude, early and middle pulses strongly suppressed E. canadensis growth and invasion. In contrast, natives generally exhibited different responses to nutrient pulses. Our study shows that plant responses are not just dependent on the presence of a resource pulse but also on its attributes. In contrast to theory and many empirical studies, our results show that resource fluctuation does not always promote plant invasion. We highlight that the attributes of resource pulses are key to understanding the impact of resource fluctuations on plant invasion.

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Identifying food web linkages between biocontrol agents of invasive plants and native species is crucial for predicting indirect non‐target effects. Biocontrol insects can integrate into food webs within recipient habitats and influence native insects through apparent competition (altering shared natural enemies) or density‐mediated exploitation competition (changing density of native plants). However, whether and how trait‐mediated exploitation competition (modifying native plant chemicals and volatiles profiles) can produce indirect non‐target effects remains largely overlooked, despite plant phenotypic responses to insect herbivory being common and widely documented. The flea beetle Agasicles hygrophila was introduced into China for management of alligator weed Alternanthera philoxeroides, but it also attacks the native congener sessile joyweed Alternanthera sessilis, which may cause indirect non‐target effects on the native tortoise beetle Cassida piperata that also feeds on sessile joyweed. Here, we examined the relationships among abundances of the flea beetle and tortoise beetle, and coverage of sessile joyweed in the field. Then, we investigated the impact of flea beetle herbivory on tortoise beetle development and oviposition, as well as on sessile joyweed primary metabolites and leaf volatiles. Tortoise beetle abundance was not related to sessile joyweed coverage, but they were less abundant on plants with more flea beetles in the field survey, and produced fewer offspring on plants with more prior flea beetle damage in the field cage experiment. Tortoise beetle development was inhibited by prior flea beetle herbivory in bioassays in enemy‐free conditions and they preferred to oviposit on sessile joyweed that had experienced little or no flea beetle damage. Flea beetle herbivory decreased sessile joyweed foliar glucose and protein, and substantially changed its leaf volatile blend. Synthesis. Our results show that the flea beetle has major indirect non‐target effects on the tortoise beetle through trait‐mediated exploitation competition, rather than apparent competition or density‐mediated exploitation competition. Our results demonstrate a new example for indirect non‐target effects of biocontrol agents. Furthermore, our results indicate that minor brief negative impacts of biocontrol agents on non‐target plants might propagate to higher trophic levels and such negative impacts can strengthen with increasing intensity of the direct non‐target effect.

Fluctuating resource availability plays a critical role in determining non‐native plant invasions through mediating the competitive balance between non‐native and native species. However, the impact of fluctuating resource availability on interactions among non‐native species remains largely unknown. This represents a barrier to understanding invasion mechanisms, particularly in habitats that harbor multiple non‐native species with different responses to fluctuating resource availability. To examine the responses of non‐native plant species to nutrient fluctuations, we compared the growth of each of 12 non‐native species found to be common in local natural areas to nutrients supplied at a constant rate or supplied as a single large pulse in a pot experiment. We found that seven species produced more biomass with pulsed nutrients compared to constant nutrients (hereafter “benefitting species”), while the other five species did not differ between nutrient enrichment treatments (hereafter “non‐benefitting species”). To investigate how nutrient fluctuations influence the interactions among non‐native plant species, we established experimental non‐native communities in the field with two benefitting and two non‐benefitting non‐native species. Compared with constant nutrient supply, the single large pulse of nutrient did not influence community biomass, but strongly increased the biomass and cover of the benefitting species and decreased those of the non‐benefitting species. Furthermore, the benefitting species had higher leaf N content and greater plant height when nutrients were supplied as a single large pulse than at a constant rate, whereas the non‐benefitting species showed no differences in leaf N content and were shorter when nutrients were supplied as a single large pulse than at a constant rate. Our results add to the growing evidence that the individual responses of non‐native species to nutrient fluctuation are species‐specific. More importantly, benefitting species were favored by nutrients coming in a pulse, while non‐benefitting ones were favored by nutrients coming constantly when they grew together. This suggests that nutrient fluctuations can mediate the competitive balance among non‐native plants and may thus determine their invasion success in a community harboring multiple non‐native plant species.

Variation in species composition among sites (beta diversity) is generally thought to be driven by environmental filtering and dispersal limitation, but the role of biotic interactions has not been sufficiently addressed. Specifically, the early species in a local community may contribute to subsequent beta diversity patterns. Exotic assemblages within native communities provide a unique opportunity to study biotic interaction mechanisms. In this study, we conducted a field survey of plants over an approximately 1800‐km transect in the middle and lower Yangtze River valley in China to study how native communities influence exotic beta diversity. The survey included 459 plots in 51 local plant communities with 40 exotic species and 103 co‐occurring native species. We also investigated how 11 environmental factors involving climate conditions, soil properties, and human activity regulate the interaction between native and exotic plants. The results showed that native diversity (Shannon–Wiener index) increased exotic beta diversity. Environmental conditions, especially monthly minimum temperature, influenced exotic beta diversity indirectly through native diversity rather than directly. Our results suggest that lower native diversity driven by environmental conditions, especially warmer temperatures, led to a decrease in composition heterogeneity of the exotic flora. Our results will help to incorporate biotic interactions into the framework of beta diversity mechanisms for local community assembly.

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