Mixture-effects on tree biomass production and soil organic C quality in a temperate plantation forest

<p>Forest restoration and afforestation on degraded lands are receiving tremendous research efforts globally as a climate change mitigation option. There is a growing interest in mixed species plantation to ensure sustainable ecosystem services and biodiversity. However, successful mixture of achieving these potential benefits is rare. We studied the polyculture of two pioneer fast growing species (i.e. <em>B. pendula</em>,  and <em>A. glutinosa</em>- of which <em>A. glutinosa</em> is N-fixing) and one shed tolerant species with slow juvenile growth (i.e. <em>F. sylvatica</em>) to examine the effects of species mixture on biomass production and quality of soil organic C stock following the replacement series approach. Standing woody biomass in polyculture demonstrated no over-yielding, presumably due to concurrent impacts of suppression of <em>F sylvatica</em> by two fast growing species and competitive reduction benefits in <em>A. glutinosa</em>. Similarly, standing fine root biomass production and turnover showed no significant mixture effect.  Although the quantity of soil organic C stock was unaffected by tree mixture, the vertical distribution of biodegradable C fractions was differed between mono and polyculture stands,  most probably due to slow decay rate of mixed litter. We found that species mixture decreased soil C lability in the upper soil layers, and increased recalcitrant C  in deep soil (>40 cm) that has enormous potential for long-term sequestration. We concluded that contrasting growth responses can result in no biomass over-yielding in polyculture stands but the mixed litter can affect soil C quality.</p><p>Key words: Mixture effects, Tree polyculture, biomass, over-yielding, C quality, recalcitrant C</p>

Characteristics of fungal community structure during the decomposition of mixed foliage litter from Pinus massoniana and broadleaved tree species in southwestern China

Aims The conifer litter is fairly recalcitrant and nutrient poor, and broadleaved litter promotes coniferous litter decomposition by increasing degradable nutrients and promoting microbial metabolism. Mixing Pinus massoniana litter and three broadleaved litters may increase the diversity and abundance of fungal decomposers compared with those in P. massoniana litter and vary depending on the number and proportion of broadleaved species included. Methods We analysed the composition and diversity of fungal communities during mixed litter decomposition in southwestern China with 35 treatments (P. massoniana, Toona sinensis, Cinnamomum camphora and Sassafras tzumu litter) using Illumina high-throughput sequencing. Important Findings The mixed litters increased fungal diversity and richness compared with those in the single-species litter, except in the following treatments: P. massoniana litter accounting for 70%–80% in the P. massoniana + T. sinensis, P. massoniana + S. tzumu + T. sinensis and P. massoniana + S. tzumu + C. camphora combinations, and P. massoniana + S. tzumu + C. camphora + T. sinensis combination with small proportion of T. sinensis litter. The diversity and richness of the 7:1:2 combination of P. massoniana + C. camphora + T. sinensis were significantly higher than those in the other treatments. Ascomycota and Basidiomycota were the dominant phyla, and Aspergillus was the most abundant genus. The decomposition of litters from one needleleaf and one broadleaved species (6:4) and one needleleaf species and two broadleaved species (broadleaved litter accounting for 30%–40%) exhibited synergistic interactions throughout the decomposition process, and the relative abundance of fungi that decompose refractory substances increased. The P. massoniana + C. camphora + T. sinensis combination and a 30%–40% broadleaf litter proportion increased fungal diversity and accelerated the decomposition of recalcitrant coniferous litter. Therefore, C. camphora and T. sinensis are a potential candidate species for mixed planting with P. massoniana.

Natural Regeneration Following Partial and Clear-Cut Harvesting in Mature Aspen-Jack Pine Stands in Eastern Canada

Over the last three decades, the ecological basis for the generalized use of even-aged silviculture in boreal forests has been increasingly challenged. In boreal mixed-wood landscapes, the diminishing proportion of conifers, to the benefit of intolerant hardwoods, has been a primary concern, coupled with the general rarefication of old-growth conifer-dominated stands. In this context, partial cutting, extended rotations and forest renewal techniques that eliminate or reduce regenerating hardwoods have been proposed as means of regaining greater conifer cover. As a result, experimentation and industrial application of various forms of both variable retention and partial harvesting are occurring across the commercial Canadian boreal forest. In this study, we compared the effects of two harvesting intensities, clearcutting and low-intensity partial cutting (removal of 25–31% of tree basal area), on hardwood and conifer regeneration levels 7–19 years following treatments in aspen (Populus tremuloides)-dominated stands and verified whether regeneration differences existed between micro-sites on and off machinery trails. The abundance of aspen regeneration increased with percent basal area removal and was positively correlated to the abundance of mature aspen prior to harvesting. The abundance of fir (Abies balsamea) regeneration after partial cutting was similar to controls and higher than after clear-cutting and was positively correlated with ground cover of mixed litter (i.e., mixture of needles and leaves) and negatively correlated with ground cover of broadleaf litter. These results suggest that it is possible in boreal mixed-woods to control aspen abundance and promote or maintain conifer regeneration through silvicultural treatments that limit canopy opening and promote mixed forest floor litter.

Effects of nitrogen deposition on litter decomposition and nutrient release mediated by litter types and seasonal change in a temperate forest

We conducted a field experiment with four levels of simulated nitrogen (N) deposition (0, 2.5, 5, and 7.5 g N m−2 yr−1, respectively) to investigate the response of litter decomposition of Pinus koraiensis (PK), Tilia amurensis (TA), and their mixture to N deposition during winter and growing seasons. Results showed that N addition significantly increased the mass loss of PK litter and significantly decreased the mass loss of TA litter throughout the 2 yr decomposition processes, which indicated that the different responses in the decomposition of different litters to N addition can be species specific, potentially attributed to different litter chemistry. The faster decomposition of PK litter with N addition occurred mainly in the winter, whereas the slower decomposition of TA litter with N addition occurred during the growing season. Moreover, N addition had a positive effect on the release of phosphorus, magnesium, and manganese for PK litter and had a negative effect on the release of carbon, iron, and lignin for TA litter. Decomposition and nutrient release from mixed litter with N addition showed a non-additive effect. The mass loss from litter in the first winter and over the entire study correlated positively with the initial concentration of cellulose, lignin, and certain nutrients in the litter, demonstrating the potential influence of different tissue chemistries.

Whole Genome Analysis of a Single Scottish Deerhound Dog Family Provides Independent Corroboration That a SGK3 Coding Variant Leads to Hairlessness

The breeds of domestic dog, Canis lupus familiaris, display a range of coat types with variation in color, texture, length, curl, and growth pattern. One trait of interest is that of partial or full hairlessness, which is found in a small number of breeds. While the standard for some breeds, such as the Xoloitzcuintli, requires sparse hair on their extremities, others are entirely bald, including the American Hairless Terrier. We identified a small, rare family of Scottish Deerhounds in which coated parents produced a mixed litter of coated and hairless offspring. To identify the underlying variant, we performed whole genome sequencing of the dam and five offspring, comparing single nucleotide polymorphisms and small insertions/deletions against an established catalog of 91 million canine variants. Of 325 homozygous alternative alleles found in both hairless dogs, 56 displayed the expected pattern of segregation and only a single, high impact variant within a coding region was observed: a single base pair insertion in exon two of SGK3 leading to a potential frameshift, thus verifying recently published findings. In addition, we observed that gene expression levels between coated and hairless dogs are similar, suggesting a mechanism other than non-sense mediated decay is responsible for the phenotype.