The Response of Plants and Mycorrhizal Fungi to Nutritionally-Heterogeneous Environments Are Regulated by Nutrient Types and Plant Functional Groups

Nutrient type and plant functional group are both important in influencing proliferation of roots or hyphae and their benefit to plant growth in nutritionally heterogeneous environments. However, the studies quantifying relative importance of roots vs. hyphae affecting the plant response to nutrient heterogeneity are lacking. Here, we used meta-analysis based on 879 observations from 66 published studies to evaluate response patterns of seven variables related to growth and morphological traits of plants and mycorrhizal fungi in nutritionally heterogeneous environments. We found that phosphorus [P] and organic fertilizer [OF] supply significantly increased shoot (+18.1 and +25.9%, respectively) and root biomass (+31.1 and +23.0%, respectively) and root foraging precision (+11.8 and +20.4%, respectively). However, there was no significant difference among functional groups of herbs (grasses, forbs, and legumes), between herbs and woody species, and between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree species in the shoot, root and mycorrhizal fungi responses to nutrient heterogeneity, except for root biomass and root foraging precision among grasses, forbs, and legumes, and mycorrhizal hyphal foraging precision between AM and ECM tree species. Root diameter was uncorrelated with neither root foraging precision nor mycorrhizal hyphal foraging precision, regardless of mycorrhizal type or nutrient type. These results suggest that plant growth and foraging strategies are mainly influenced by nutrient type, among other factors including plant functional type and mycorrhizal type.

Root foraging of birch and larch in heterogeneous soil nutrient patches under water deficit

Water and nutrient are two critical factors that limit plant growth to spatial-temporal extents. Tree root foraging behavior has not received adequate attention in heterogeneous soil environments in temperate forest under drought pressure. In this study, birch (Betula platyphylla) and larch (Larix olgensis) seedlings were raised in pots in a split-root system with artificially heterogeneous soil environments to study the root foraging response to drought. Potted space was split into two halves where substrates were mixed with fertilizers in 67.5 mg nitrogen (N) plant-1 (N-P2O5-K2O, 14-13-13) to both halves as to create a homogeneous condition. Otherwise, a rate of 135 mg N plant-1 of fertilizers was delivered to a random half to create a heterogeneous condition. Half of seedlings were fully sub-irrigated every three days with the other half received the drought treatment by being watered every six days. Both birch and larch seedlings showed greater net shoot growth and biomass increment in well-watered condition, while root morphology was promoted by drought. Both species placed more fine roots with higher root N concentration in nutrient-enriched patches. In the heterogeneous pattern, birch showed a higher foraging precision assessed by biomass and greater foraging plasticity assessed in morphology and physiology. In contrast, larch seedlings had higher root N concentration in the well-watered condition. Neither species showed a significant response of N utilization to the heterogeneous pattern, but both used more N when water supply was improved. Overall, birch is better at acclimating to heterogeneous soil conditions, but its ability to seize N was lower than larch when drought was alleviated.

Root Foraging Precision of Pinus pumila (Pall.) Regel Subjected to Contrasting Light Spectra

Root foraging behavior in heterogeneous patterns of soil nutrients is not well understood for undergrowth in alpine forests, where light spectra may generate an interactive effect on root foraging precision. A dwarf alpine species, Pinus pumila (Pall.) Regel., was cultured in pots where nitrogen (N)–phosphorus (P)–potassium (K) nutritional granules (N–P2O5–K2O, 14–13–13) were added to both halves of an inner space at a rate of 67.5 mg N (homogeneous) or 135 mg N to a random half (heterogeneous). Potted seedlings were subjected to either a green-and-blue light spectrum with a red-to-green light ratio of 4.24 (15.3% red, 64.9% green, and 19.8% blue) or a red-light enriched spectrum (69.4% red, 30.2% green, and 0.4% blue) both at irradiations of 200.43 µmol m−2 s−1. The root foraging precision was assessed by the difference in the fine root morphology or weight between the two halves. The foraging precision was assessed by both fine root length and surface area and was promoted in seedlings subjected to the heterogeneous pattern in the red-light enriched spectrum. Seedlings subjected to the green-and-blue light spectrum showed lower shoot growth, biomass, and root morphology but had higher shoot and root N and P concentrations. The heterogenous pattern resulted in greater seedling growth and fine root morphology as well as N and P concentrations compared to the homogeneous pattern. We conclude that P. pumila has a strong ability to forage nutrients in heterogenous soil nutrients, which can be further promoted by a spectrum with higher red-light proportions.

Root Foraging Precision: Do Experimental Conditions Matter?

Purpose: Root foraging precision, i.e., preferential root proliferation in nutrient-rich patches in heterogeneous soil, contributes significantly to plant nutrient acquisition. The ability to forage is usually studied experimentally, although often under different conditions. It remains unclear whether different experimental conditions affect root foraging precision. We studied the effect of experiment duration, pot size and root separation on root foraging precision and the appropriateness of using root foraging as species-specific values in databases and meta-analyses.Methods: We cultivated three perennial species in pots with spatially heterogeneous nutrient supplies and manipulated the experiment duration (4 – 10 weeks). We partly replicated the experiment in two consecutive years. In two of the three species we compared outcomes when root types were separated and unseparated, and for one species we also manipulated pot size. We assessed the effects of the manipulated factors on foraging precision expressed as the ratio of root biomass in nutrient-rich and poor patches.Results: Root foraging precision was not affected by experiment duration or pot size. Separating roots to use only the fine ones for root foraging assessment amplified foraging precision values and reduced their intraspecific variation.Conclusions: Our study investigated various methods of the root foraging research and their impact on the root foraging precision. Root foraging precision is invariable to the studied factors, therefore it is suitable as a species-specific trait, if the effect of other factors (such as nutrient patch characteristics) is taken into account.

The root-fungus interplay in foraging for heterogeneous sources

<p>The distribution of nutrients in the soil is very heterogeneous at different scales relevant to plant roots, and plants respond to this heterogeneity by the architecture of the root system. The ability to form the root system in terms of the most effective nutrient uptake differs among species. Moreover, over 70% of terrestrial plants create arbuscular mycorrhizal symbiosis, which helps them to acquire nutrients from the soil. It has been shown that plants with mycorrhizal symbiosis acquire nutrients from heterogeneous soil differently than plants without mycorrhizal fungi. Our study aims to estimate the link between the root and fungal foraging for heterogeneous sources using an experimental approach. We show the root foraging precision of nine plant species together with three fungal species in the heterogeneous soil environment. The first results suggest that root foraging is not affected by the presence of mycorrhizal fungi and that fungal foraging may form in the opposite direction than root foraging.</p>

Where do the good foragers live?

<p>Plant species differ in their ability to preferentially grow their roots into nutrient-rich patches in the substrate - this aspect of plant phenotypic plasticity is known as "root foraging". Using a set of approx. 80 Central European herbaceous species of open habitats we show how the root foraging precision of the species is linked to their usual environment. We have obtained the root foraging data experimentally and we combine them with tabelar data that describe species' preference for soil moisture and soil nutrients availability (Ellenberg's Indicator Values), species' ability to occupy frequently disturbed habitats and typical habitats of the species in general. </p>

Root Foraging Ability for Phosphorus in Different Genotypes Taxodium ‘Zhongshanshan’ and Their Parents under Phosphorus Deficiency

The phosphorus (P) deficiency is the one of the key constraints for Taxodium ‘Zhongshanshan’ afforestation. A hydroponic experiment was conducted to explore root foraging ability for P in different genotypes of Taxodium ‘Zhongshanshan’ (T.‘Zhongshanshan’) and their parents (T.mucronatum and T.distichum). Five P levels of CK (31 mg/L), P15 (15 mg/L), P10 (10 mg/L), P5 (5 mg/L), and P0 (0 mg/L) were set up as the P deficiency stress treatment. The plant P contents, root morphological indices, and plant growth traits of different taxodium genotypes were measured. Meanwhile, the root foraging ability for P was evaluated with the membership function method in combination with weight. Results showed that: (1) Except the plant P content, the root morphology, plant net biomass, and height showed significant differences among the different genotypes (p < 0.05); the P deficiency stress had no significant influence on root morphology, but a significant influence on plant net biomass and height and P content; (2) T.mucronatum and T.‘Zhongshanshan’302 had relatively lower values of root length, root surface area, root volume, and plant net biomass, but had no difference of plant P content with the other genotypes; (3) T.mucronatum and T.‘Zhongshanshan’302 had higher root foraging ability for P than the other genotypes; (4) the stepwise regression analysis revealed the root volume as the main factor significantly influencing the root foraging ability. This study concluded that different genotypes of T.’Zhongshanshan’ and their parents had different root foraging ability for P, and breeding and screening the fine varieties is conducive for the afforestation in P-limited areas.