Life at the conservative end of the leaf economics spectrum: intergeneric variation in the allocation of phosphorus to biochemical fractions in species of Banksia (Proteaceae) and Hakea (Proteaceae).

In severely phosphorus (P)-impoverished environments, plants have evolved to use P very efficiently. Yet, it is unclear how P allocation in leaves contributes to their photosynthetic P-use efficiency (PPUE) and position along the leaf economics spectrum (LES). We address this question in 10 species of Banksia and Hakea, two highly P-efficient Proteaceae genera. We characterised traits in leaves of Banksia and Hakea associated with the LES: leaf mass per area, light-saturated photosynthetic rates, P and nitrogen concentrations, and PPUE. We also determined leaf P partitioning to five biochemical fractions (lipid, nucleic acid, metabolite, inorganic and residual P) and their possible association with the LES. For both genera, PPUE was negatively correlated with fractional allocation of P to lipids, but positively correlated with that to metabolites. For Banksia only, PPUE was negatively correlated with residual P, highlighting a strategy contrasting to that of Hakea. Phosphorus-allocation patterns significantly explained PPUE but were not linked to the resource acquisition vs resource conservation gradient defined by the LES. We conclude that distinct P-allocation patterns enable species from different genera to achieve high PPUE and discuss the implications of different P investments. We surmise that different LES axes representing different ecological strategies coexist in extremely P-impoverished environments.

Leaf phosphorus allocation to chemical fractions and its seasonal variation in south-western Australia is a species-dependent trait.

South-western Australia is a global biodiversity hotspot and has some of the oldest and most phosphorus (P)-impoverished soils in the world. Proteaceae is one of the dominant P-efficient plant families there, but it is unknown how leaf P concentrations and foliar P allocation of Proteaceae and coexisting dominant plant families vary between seasons and habitats. To investigate this, we selected 18 species from Proteaceae, Myrtaceae and Fabaceae, six from each family, in two habitats from Alison Baird Reserve (32°1'19''S 15°58'52''E) in Western Australia. Total leaf P and nitrogen (N) concentrations, leaf mass per area, photosynthetic rate, pre-dawn leaf water potential and foliar P fractions were determined for each species both at the end of summer (March 2019 and early April 2020) and at the end of winter (September 2019). Soil P availability was also determined for each site. This is the very first study that focused on seasonal changes of foliar P fractions from different P-impoverished environments in three plant families. However, contrary to our expectation, we found little evidence for convergence of foliar P allocation within family, season or habitat. Each species exhibited a specific species-dependent pattern of foliar P allocation, and many species showed differences between seasons. Native plants in south-western Australia converged on a high photosynthetic P-use efficiency, but each species showed its own unique way associated with that outcome.

Aging rate, environmental risk and production efficiency of the low-density polyethylene (LDPE) films with contrasting thickness in irrigated region.

Physical thickness of low-density polyethylene (LDPE) films might determine the release rate of phthalic acid esters (PAEs) & structural integrity and affect production efficiency. However, this critical issue is still unclear and little reported. Aging effects were evaluated in LDPE films with the thickness of 0.006, 0.008, 0.010 and 0.015 mm in a maize field of irrigation region. The Scanning electron microscope (SEM) results showed that the proportion of damaged area (Dam) to total area of LDPE films was massively lowered with increasing thickness after aging. The highest and lowest Dam was 32.2% and 3.5% in 0.006 and 0.015 mm films respectively. Also, the variations in peak intensity of asymmetric & symmetrical stretching vibrations (ASVI & SSVI) were detected using Fourier transform infrared spectrum (FTIR), indicating that the declines in peak intensity tended to be slower with thickness. Interestingly, the declines in physical integrity were tightly associated with increasing exhalation rate of PAEs. Average releasing rate of PAEs was 38.2%, 31.4%, 31.5% and 19.7% in LDPE films from 0.006 to 0.015 mm respectively. Critically, thicker film mulching can lead to greater soil water storage at plough layer (SWS-PL) and better thermal status, accordingly harvesting higher economic benefit. Therefore, LDPE film thickening may be a solution to reduce environmental risk but improve production efficiency in arid region.

Fate of plastic film residues in agro-ecosystem and its effects on aggregate-associated soil carbon and nitrogen stocks.

Biodegradable (Bio) plastic films are widely viewed as promising alternative products of low-density polyethylene (LDPE) films to minimize plastic debris accumulation and pollution in agroecosystems. Yet, this speculation indeed lacks of sufficient evidences. We conducted a landfill investigation on the aging characteristics of Bio and LDPE plastic films in maize field, and the effects on soil aggregate composition and carbon & nitrogen stocks. The degradation rate of Bio film was up to 41.1% while that of LDPE film was zero. Scanning electron microscope (SEM) showed that the crack formation of Bio film had a pronounced domino effect, and FTIR showed that old Bio film displayed an extra wide peak threshold ranging from 3000 to 3500 cm-1. Particularly, the abundance of microplastics was elevated with the increased plastic residues, and the increment mostly resulted from Bio residues. Critically, plastic residues significantly lowered the soil macro-aggregates (>0.25 mm) proportion, while increasing that of micro-aggregates (0.1-0.25 mm) in LDPE, and silt/clay fraction (<0.1 mm) in Bio respectively. They significantly promoted total nitrogen content of the aggregates with the same size, but decreased the organic carbon content, dramatically lowering the C/N. Therefore, we first identified the fate of plastic film residues in agroecosystems and revealed the serious deficiencies of Bio plastic film.

[Impact of habitats on rodent-mediated seed fates of Quercus aliena var. acuteserrata.] / ç”Ÿå¢ƒå¯¹å•®é½¿åŠ¨ç‰©ä»‹å¯¼ä¸‹é”é½¿æ§²æ Žç§å­å‘½è¿çš„å½±å“.

Disturbance is the driving force of forest succession, which can change forest structure and surface vegetation. Disturbance also affects rodent-mediated seed dispersal. In this study, numbered plastic tags were used to examine the responses of rodent dispersal behavior to the fates of Quercus aliena var. acuteserrata acorns at three habitats formed by different artificial disturbances in pine-oak mixed forests in the Qinling Mountains, i.e., unlogged stand, stand in the third year after tending thinning, and bare land. The results showed that seed removal rate from stands in the third year after tending was significantly higher than that in the other two habitats. The proportion of predation in bare land was significantly lower than that in the unlogged stand (25.0%) and in the stand in the third year after tending thinning (36.3%). In the third year after tending thinning, the seed predation rate after seed moving was significantly higher than those in the unlogged stand (17.3%) and bare land (5.0%). Moreover, the proportion of scatter hoarding after removal was also highest in the stand in the third year after tending thinning (4.3%). The longest average dispersal distance (26 m) occurred in the stand in the third year after tending thinning, which was significantly longer than those at the other two habitats. Therefore, the different habitat types significantly influenced the initial seed dispersal process by rodents, with consequences on the rates of seedling establishment. Habitat types affected the foraging strategies of rodents, thereby leading to different seed dispersal modes and natural regeneration patterns in the forest.