You are what you eat: nutrient and water relations between mistletoes and hosts

Nitrogen-fixing and non-nitrogen-fixing legume plants differ in leaf nutrient concentrations and relationships between photosynthetic and hydraulic traits

Legumes account for a significant proportion of plants in the terrestrial ecosystems. Nitrogen (N)-fixing capability of certain legumes is a pivotal trait that contributes to their ecological dominance. Yet, the functional traits and trait relationships between N-fixer and non-N-fixer legumes are poorly understood. Here, we investigated 27 functional traits associated with morphology, nutrients, hydraulic conductance and photosynthesis in 42 woody legumes (19 N-fixers and 23 non-N-fixers) in a common garden. Our results showed that N-fixers had higher specific leaf area, photosynthetic phosphorus (P)-use efficiency, leaf N, and iron concentrations on both area and mass basis, N/P ratio, and carbon (C) to P ratio, but lower wood density, area-based maximum photosynthetic rate (Aa), photosynthetic N-use efficiency, leaf mass- and area-based P and molybdenum and area-based boron concentrations, and C/N ratio, compared with non-N-fixers. The mass-based maximum photosynthetic rate (Am), stomatal conductance (gs), intrinsic water-use efficiency (WUEi), mass- and area-based leaf potassium and mass-based boron concentrations, leaf hydraulic conductance (Kleaf), and whole-shoot hydraulic conductance (Kshoot) showed no difference between N-fixers and non-N-fixers. Significant positive associations between all hydraulic and photosynthetic trait pairs were found in N-fixers, but only one pair (Kshoot-Aa) in non-N-fixers, suggesting that hydraulic conductance plays a more important role in mediating photosynthetic capacity in N-fixers compared with non-N-fixers. Higher mass-based leaf N was linked to lower time-integrated gs and higher WUEi among non-N-fixer legumes or all legumes pooled after phylogeny was considered. Moreover, mass-based P concentration was positively related to Am and gs in N-fixers, but not in non-N-fixers, indicating that the photosynthetic capacity and stomatal conductance in N-fixers were more dependent on leaf P status than in non-N-fixers. These findings expand our understanding of the trait-based ecology within and across N-fixer and non-N-fixer legumes in tropics.

The associational effects of host plant and mistletoe functional traits on leaf herbivory in mistletoe

Associational effects are a phenomenon in which herbivore damage on co-occurring plant species is influenced by neighboring plants. Mistletoes are a group of shrubs that obtain nutrients from host plants through haustoria. Despite the potential for mistletoe herbivory to be affected by associational effects with their hosts, the effects of host and mistletoe functional traits on mistletoe herbivory have been largely overlooked. This study aimed to evaluate the associational effects of host plants and the direct effects of mistletoe functional traits on mistletoe herbivory. To achieve this, we measured leaf herbivory and leaf traits of three mistletoe species (Dendrophthoe pentandra, Scurrula chingii var. yunnanensis, and Helixanthera parasitica) and their associated 11 host species during both dry and wet seasons. Our results showed that leaf herbivory of D. pentandra and S. chingii var. yunnanensis differed significantly on their respective host species, but H. parasitica did not. The relationships between mistletoe and the paired host herbivory differed between seasons, with a stronger positive relationship observed during the dry season. Furthermore, significant relationships were observed between paired leaf carbon, leaf nitrogen, and condensed tannin in mistletoes and their host plants, indicating that host plants can affect mistletoes' leaf functional traits. A group of mistletoe leaf traits provided significant predictions for leaf herbivory: leaves with higher leaf thickness and leaf total nitrogen showed higher herbivory. Overall, our study reveals that mistletoe leaf herbivory is directly affected by its leaf traits and indirectly affected by host associational effects, primarily through changes in mistletoes' leaf traits.

Resource availability and parasitism intensity influence the response of soybean to the parasitic plant Cuscuta australis

Introduction

Parasitic plants can damage crop plants and consequently cause yield losses and thus threaten food security. Resource availability (e.g., phosphorus, water) has an important role in the response of crop plants to biotic attacks. However, how the growth of crop plants under parasitism are affected by environmental resource fluctuation is poorly understood.

Methods

We conducted a pot experiment to test the effects of the intensity of Cuscuta australis parasitism and the availability of water and phosphorus (P) on soybean shoot and root biomass.

Results and discussion

We found that low-intensity parasitism caused ~6% biomass reduction, while high-intensity parasitism caused ~26% biomass reduction in soybean. Under 5-15% water holding capacity (WHC), the deleterious effect of parasitism on soybean hosts was ~60% and ~115% higher than that under 45-55% WHC and 85-95% WHC, respectively. When the P supply was 0 μM, the deleterious effect of parasitism on soybean was 67% lower than that when the P supply was 20 μM. Besides, the biomass of C. australis was highest when both the water and the P availability were lowest. Cuscuta australis caused the highest damage to soybean hosts under 5 μM P supply, 5-15% WHC, and high-intensity parasitism. Additionally, C. australis biomass was significantly and negatively related to the deleterious effect of parasitism on soybean hosts and to the total biomass of soybean hosts under high-intensity parasitism, but not under low-intensity parasitism. Although high resource availability can promote soybean growth, the two resources have different impacts on the response of hosts to parasitism. Higher P availability decreased host tolerance to parasites, while higher water availability increased host tolerance. These results indicate that crop management, specifically water and phosphorus supply, can efficiently control C. australis in soybean. To our best knowledge, this appears to be the first study to test the interactive effect of different resources on the growth and response of host plants under parasitism.