Functional Trait Plasticity but Not Coordination Differs in Absorptive and Transport Fine Roots in Response to Soil Depth

Relationship between the roots of Hippophae rhamnoides at different stump heights and the root microenvironment in feldspathic sandstone areas

Background

To solve the withering of Hippophae rhamnoides plantation in the feldspathic sandstone areas of Inner Mongolia and to promote the regeneration, rejuvenation, and sustainability of H. rhamnoides forests.

Methods

We stumped aging H. rhamnoides trees at the ground heights of 0, 10, 15, and 20 cm (S1, S2, S3, and S4, respectively) and utilized unstumped trees as the control (CK). We then analyzed the effects of the different stump heights on the roots and the root microenvironment of H. rhamnoides and the relationship between the roots and the root microenvironment in the stumped H. rhamnoides.

Results

The root fractal features, root branching rate, root length, root soluble proteins, soil moisture content, and soil nutrients among the different treatments were ranked as S3>S2>S1>S4>CK (P < 0.05). The root topological index, root proline, and malondialdehyde among the different treatments were ranked as S3<S2<S1<S4<CK (P < 0.05). The topological indices of S1, S2, S3, S4, and CK were 0.80, 0.86, 0.89, 0.94, and 0.98, respectively, and all were near 1. This result indicated a typical fishtail-shaped branching structure. The root length and root fractal dimensions were primarily affected by the positive correlation of the soil moisture content and the soil organic matter, and the root topological index was primarily affected by the negative correlation of the root proline. Root nutrients were dominant in the changes in the root architecture, while soil moisture and nutrients played supporting roles. These results indicated that stumping can promote plant root growth and root nutrient accumulation, thereby improving soil moisture and the soil nutrient distribution, and the S3 treatment had the greatest impact on the H. rhamnoides roots and root microenvironment. Therefore, the 15 cm stump height treatment should be implemented for withering H. rhamnoides in feldspathic sandstone areas to promote vegetation restoration.

The Hierarchy of Protoxylem Groupings in Primary Root and Their Plasticity to Nitrogen Addition in Three Tree Species

Protoxylem grouping (PG), a classification based on the number of protoxylem poles, is a crucial indicator related to other functional traits in fine roots, affecting growth and survival of individual root. However, within root system, less is known about the arrangement of PG. Moreover, the responses of PG to fertilization are still unclear. Here, we selected three common hardwood species in Northeast China, Juglans mandshurica, Fraxinus mandshurica, and Phellodendron amurense, conducted root pruning and nutrient addition. In this study, we analyzed the PG, morphology, and other anatomy traits of newly formed root branches. The results showed all root length, diameter, and stele, as well as hydraulic conductivity, were significantly positive related to the PG number, and the PG number generally decreased with ascending root developmental order; these patterns were independent of species and fertilization. Additionally, we also found the plasticity of PGs to environmental changes, in terms of the increased frequency of high PG roots after fertilization, significantly in J. mandshurica and F. mandshurica. Therefore, the heterogeneity, hierarchy, and plasticity of individual roots within root system may be widespread in woody plants, which is of great significance to deepen our understanding in root growth and development, as well as the belowground ecological process.

How Does Deforestation Affect the Growth of Cypripedium (Orchidaceae) Species? A Simulation Experiment in Northeast China

Due to wild habitat destruction, Cypripedium is among the most endangered groups in China. Determining how Cypripedium respond to environmental changes is curial to their conservation. However, less is known about the effect of deforestation on the growth of Cypripedium. In this study, we selected four Cypripedium species in Northeast China, and conducted conservation-based transplantation simulating deforestation to explore the impact of increased light intensity on the growth of Cypripedium. After three years, the maximum net photosynthetic rate was decreased by 15.9%, 11.5%, 13.6% and 5.3% for C. calceolus L., C. guttatum Sw., C. macranthos Sw. and C.×ventricosum Sw., respectively, resulting in poor viability, manifesting as shorter and thinner shoots, and smaller leaves. Unexpectedly, no significant traits shifts were found in the roots across four species, which may be related to the long root lifespan and conservation. Our research confirmed that increased light intensity caused by deforestation would lead to an increase in respirate cost and a decrease in photosynthate accumulation, and consequently the recession of plant growth. Except for habitat loss, individual plant reduction caused by deforestation could be responsible for the population decline of Cypripedium.

Root anatomy helps to reconcile observed root trait syndromes in tropical tree species

PREMISE

Studying the organization of functional traits in plant leaves and stems has revealed notable patterns linking function and form; however, evidence of similarly robust organization in root tissues remains controversial. We posit that anatomical traits in roots can provide insight on the overall organization of the root system. We hypothesized that size variation in the tissue outside the stele is related in a nonlinear fashion with functional traits associated with direct resource uptake, including a negative relationship with root architectural traits, and that similar relationships detected in tropical areas also hold true in other biomes.

METHODS

We addressed our hypotheses using empirical data from 24 tropical tree species in French Guiana, including anatomical measurements in first order roots and functional trait description for the entire fine root system. In addition, we compiled a global meta-analysis of root traits for 500+ forest species across tropical, subtropical, and temperate forests.

RESULTS

Our results supported the expected nonlinear relationships between cortical size and morphological traits and a negative linear trend with architectural traits. We confirmed a global negative relationship among specific root length (SRL), diameter, and tissue density, suggesting similar anatomical constraints in root systems across woody plants. However, the importance of factors varies across biomes, possibly related to the unequal phylogenetic representation across latitudes.

CONCLUSIONS

Our findings imply that the rhizocentric hypothesis can be a valuable approach to understand fine root trait syndromes and the evolution of absorptive roots in vascular plants.