Change in soil carbon following afforestation

Global forest resources assessment 2000 : main report

Hawksworth, D. L., and Rossman, A. Y. 1997. Where are all the undescribed fungi? Phytopathology 87:888-891. The hypothesis that there are 1.5 m illion fungal species on Earth, of which only about 70,000 are described, implies that 1.43 m illion remain undescribed. The recognition that many new species have yet to be found is of fundamental importance to plant pathologists, agronomists, and plant regulatory officials, among others, who continue to encounter diseases caused by previously unknown or understudied fungi. Unexplored habitats with their arsenal of unknown fungi are also of interest to those searching for novel organisms for use in biological control or for their pharmaceutical attributes. This paper presents data on the expected numbers of fungi in some relatively unexplored habitats, such as tropical forests, and those obligately associated with plants, lichens, and insects. In addition to undiscovered species, many have been collected but remain lost or hidden as named species and ignored for lack of modern characterization; others have been collected and recognized as new species but remain undescribed. Some fungal species are unrecognized within erroneously circumscribed species, often based on presumed host specificity, while others exist as biological species but remain buried within those broadly defined species for lack of gross morphological characterization. From these data, one must conclude that enormous numbers of unrecognized fungi can be found almost everywhere, including one’s own backyard.

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Where are all the undescribed fungi

The decline in aboveground wood production after canopy closure in even-aged forest stands is a common pattern in forests, but clear evidence for the mechanism causing the decline is lacking. The problem is fundamental to forest biology, commercial forestry (the decline sets the rotation age), and to carbon storage in forests. We tested three hypotheses about mechanisms causing the decline in wood growth by quantifying the complete carbon budget of developing stands for over six years (a full rotation) in replicated plantations of Eucalyptus saligna near Pepeekeo, Hawaii. Our first hypothesis was that gross primary production (GPP) does not decline with stand age, and that the decline in wood growth results from a shifft in partitioning from wood production to respiration (as tree biomass accumulates), total belowground carbon allocation (as a result of declining soil nutrient supply), or some combination of these or other sinks. An alternative hypothesis was that GPP declines with stand age and that the decline in aboveground wood production is proportional to the decline in GPP. A decline in GPP could be driven be reduced canopy leaf area and photosynthetic capacity resulting from increasing nutrient limitation, increased abrasion between tree canopies, lower turgor pressure to drive foliar expansion, or hydraulic limitation of water flux as tree height increases. A final hypothesis was a combination of the first two: GPP declines, but the decline in wood production is disproportionately larger because partitioning shifts as well. We measured the entire annual carbon budget (aboveground production and respiration, total belowground carbon allocation [TBCA], and GPP) from 0.5 years after seedling planting through 6 1/2 years (when trees were ~25m tall). The replicated plots included two densities of trees (1111 trees/ha and 10 000 trees/ha) to vary the ratio of canopy leaf mass to wood mass in the individual trees, and three fertilization regimes (minimal, intensive, and minimal followed by intensive after three years) to assess the role of nutrition in shaping the decline in GPP and aboveground wood production. The forest closed its canopy in 1-2 years, with peak aboveground wood production, coinciding with canopy closure, of 1.2-1.8 kg C.m-2yr-1. Aboveground wood production declined from 1.4 kg C.m-2yr-1 at age 2 to 0.60 kg C.m-2yr-1 at age 6. Hypothesis 1 failed: GPP declined from 5.0 kg C.m-2yr-1 at age 2 to 3.2 kg C.m-2yr-1 at age 6. Aboveground woody respiration declined from 0.66 kg C.m-2yr-1 at age 2 to 0.22 kg C.m-2yr-1 at age 6 and TBCA declined from 1.9 kg C.m-2yr-1 at age 2 to 1.4 kg C.m-2yr-1 at age 6. Our data supported hypothesis 3: the decline in aboveground wood production (42% of peak) was proportionally greater than the decline in canopy photosynthesis (64% of peak). The fraction of GPP partitioned to belowground allocation and foliar respiration increased with stand age and contributed to the decline in aboveground wood production. The decline in GPP was not caused by nutrient limitation, a decline in leaf area or in photsynthetic capacity, or (from a related study on the same site) by hydraulic limitation. Nutrition did interact with the decline in GPP and aboveground wood production, because treatments with high nutritient availablity declined more slowly than did our control treatment, which was fertilized only during stand establishment.

https://www.nrs.fs.fed.us/pubs/jrnl/2004/rm_2004_ryan_001.pdf

An experimental test of the causes of forest growth decline with stand age

https://fs.fed.us/global/iitf/pubs/ja_iitf_1999_parrotta001.pdf

Productivity, nutrient cycling, and succession in single- and mixed-species plantations of Casuarina equisetifolia, Eucalyptus robusta, and Leucaena leucocephala in Puerto Rico

Residues from harvest of eucalypt plantations represent a significant proportion of site organic matter and nutrients, and their management may influence longer term plantation productivity through changes in soil organic matter and nutrient supply. Experiments at two sites in south-western Australia were established to investigate the effects of harvest residue management on soil fertility and plantation productivity. The sites were a relatively fertile red earth, and a poorer-fertility grey sand. Harvest residue treatments were burning, complete removal of the above-ground material, retention and uniform distribution on site, and double the normal quantity of residues retained and distributed on site. Soil microbial biomass, an indicator of longer term (potentially several rotations) impacts of management on soil organic matter, was measured 1 and 5 years after planting. Retention of residues had minimal influence on total soil C and N, or C oxidized by 333 mM permanganate, but it significantly increased surface soil (0–5 cm) microbial biomass carbon (MBC) and nitrogen (MBN), as well as increasing the MBC and MBN quotients (ie. MBC and MBN as a proportion of the total soil C and N). Effects of residue management on MBC and MBN were generally highly significant 1 year after establishment, but differences between treatments had decreased after 5 years. Residue retention significantly increased MBC at both sites down to 20 cm depth, and significantly increased MBN at the red earth site at 1 year after establishment, but effects at 5 years were only evident in the surface (0–5 cm) soil. At 1 year, MBN in the surface (0–5 cm) soil was more responsive to residue retention than MBC, as the MBN quotient increased more than 2-fold at the red earth site, compared with only a 30% increase in MBC quotient. Higher MBC and MBN levels are due to greater availability of substrate derived from residues early in the rotation. The effect of residue management on microbial biomass was reduced at 5 years, and confined to the surface soil (0–5 cm), suggesting that availability of the organic material from the residues had declined. The decline was mainly due to utilization by the microbial biomass (respiration) or conversion to less labile forms.

Eucalyptus globulus harvest residue management effects on soil carbon and microbial biomass at 1 and 5 years after plantation establishment

A checklist of fungi recorded on Eucalyptus.

Organic matter accretion, decomposition and mineralisation.

The species of Ganoderma recorded from India as causing diseases of perennial crops are listed, and their host range and taxonomy discussed. Four new hosts of G. lucidum are also reported. A decline in productivity and the death of trees are the main economic impacts due to Ganoderma diseases, and the fungus is identified as a serious pathogen of cash crops, forest plantations and trees in natural forests in the country. Ganoderma diseases have been recorded on 144 hosts in India, the major pathogens being G. lucidum and G. applanatum. G. lucidum has been recorded on 91 hosts, and appears to cause the most widespread diseases. Identification has largely been made from morphological and cultural characters, and the names currently in use should therefore be treated with caution. Cultural methods of disease control are largely inefficient in minimising inoculum pressure and in reducing the disease incidence. Chemical methods in combination with soil amendments form short-term solutions for managing the disease and improving productivity. The immediate priorities for developing an efficient management system for Ganoderma diseases in India are: (1) a thorough understanding of the etiology and epidemiology of the diseases on different hosts, (2) clarifying current ambiguity in species names, (3) assessing the inter-relationships between populations of Ganoderma on different hosts and (4) developing tools for early detection of diseases in important crops.

Ganoderma diseases of perennial crops in India--an overview.

Growth and soil N supply in young Eucalyptus tereticornis stands at two sites in Kerala, India, were examined in response to cover cropping with three legume species (Pueraria phaseoloides, Stylosanthes hamata, and Mucuna bracteata). The effects of legume residues on soil N supply were investigated in a long-term (392 day) laboratory incubation using leaching micro-lysimeters. Residues from the eucalypt and legume species had different rates of net N release during the laboratory incubation. Net N release was significantly related to residue N concentration (R2 =0.94), the C:N ratio (R2 =0.91), the lignin:N ratio (R2 =0.83), and the (lignin + soluble polyphenol):N ratio (R2 =0.95). Nitrogen release rates declined in the order Mucuna > Pueraria > Eucalyptus > Stylosanthes. There was no net N release from Stylosanthes residues during the 392-day laboratory incubation, whereas Mucuna and Pueraria released N throughout the incubation period. Net N release from mixtures of legume and eucalypt residues was not additive in the early phase of the incubation, probably because eucalypt residues initially immobilized a portion of the legume-derived N in addition to the soil-derived N. Legume establishment had no significant effect on tree growth at one site (Kayampoovam), but resulted in depressed tree growth at the lower rainfall site (Punnala) at 18 months. There were no significant treatment effects on growth at Punnala after that time. Cover cropping with legumes during the early phase of forest plantation growth may be a useful mechanism to enhance soil N supply and optimize the synchrony between N supply and tree N uptake. Although these effects did not translate into improved plantation growth in the 3 years of this study, improved soil organic matter and N fertility may help ensure sustainable productivity over several rotations in the future. This study showed that the effect of legumes on N dynamics varies markedly with legume species. This, together with other factors (e.g. competition with trees, N fixation capacity), will be important in selecting suitable species for cover cropping in forest plantations.

K. V. Sankaran

Papers

Eucalyptus globulus harvest residue management effects on soil carbon and microbial biomass at 1 and 5 years after plantation establishment

A checklist of fungi recorded on Eucalyptus.

Organic matter accretion, decomposition and mineralisation.

Ganoderma diseases of perennial crops in India--an overview.

Legume cover cropping effects on early growth and soil nitrogen supply in eucalypt plantations in south-western India