Seasonal litterfall composition and carbon and nitrogen returns in New Zealand shrubland

Mānuka–kānuka shrubland is an important carbon (C) sink in New Zealand, yet little is known about C cycling within these systems. The objective of our work was to assess seasonal litterfall rates, composition, and C and nitrogen (N) inputs in mixed mānuka (Leptospermum scoparium J.R. Forst & G. Forst.) and kānuka (Kunzea ericoides var. ericoides (A.Rich) J.Thompson) stands. Litterfall was collected for 2years at Tongariro National Park (NP) and Stoney Creek, Wairarapa (SC), separated into leaf, twig, bark, seed and ‘other’, and the C and N content of each component measured. Total litterfall was between 3557 and 4443kgha–1year–1, of which leaf material contributed 46–67%. Litterfall peaked during spring–summer months at both sites, and the overall litterfall rate was greater (P < 0.001) at SC than NP. Litterfall at SC contained greater (P < 0.001) amounts of ‘other’ due to higher undergrowth contributions, and also greater seed fall (P < 0.001), possibility due to the lower altitude at SC. The proportion of leaf material in litterfall also peaked during summer (P < 0.001). C inputs in the total litter were 1941–2448kgCha–1year–1 and N inputs ranged between 28 and 37kgNha–1year–1. There was little seasonal difference in C and N contents and the majority of both C and N inputs in litterfall were in the leaf material (P < 0.001). C inputs peaked during summer, but N inputs were closely aligned with total litterfall maximums during spring–summer. The leaf:wood ratio was 1.9 at both sites, indicating litter quality was consistent at both stands, regardless of differences in composition. Although the sites had similar rainfall and shrub ages, the rate of total litterfall differed, reflecting the potentially site-specific nature of litterfall in mānuka–kānuka shrubland. Further work is needed assessing litterfall and degradation rates across New Zealand to establish if mānuka–kānuka shrublands would remain carbon sinks under climate change.

Net exchange of greenhouse gases from soils in an unimproved pasture and regenerating indigenous Kunzea ericoides shrubland in New Zealand

Monthly measurements of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were made at 3 sites along a sequence of naturally regenerating Kunzea ericoides shrubland in New Zealand, consisting of unimproved pasture (UP), young (8–12 years) Kunzea trees (YK), and old (80 years) Kunzea trees (OK). The CO2 flux at a base temperature of 10°C was highest at the OK site (0.51 g CO2/m2.h) and lowest at the UP site (0.26 g CO2/m2.h). Values of CO2 flux were regulated by soil temperature (Ts) throughout the year, and water availability modified the response to Ts when root-zone water content, (θ), fell below 0.27–0.29 m3/m3 in spring and summer. The soils were mostly CH4 sinks, although there were net CH4 emissions during wet periods at the YK site. The maximum CH4 flux at the YK site was –49.7 μg CH4/m2.h compared with –33.4 μg CH4/m2.h for the UP (and –90.4 μg CH4/m2.h for OK), indicating the potential for rapid recovery of methanotrophic populations in the YK shrubland over 8–12 years. However, on an annual basis our data suggest that CH4 oxidation rates decrease as land reverts from unimproved pasture to shrubland. Methane oxidation rates were strongly dependent on θ and only weakly dependent on Ts. Measurements of N2O fluxes were below the minimum detectable limit throughout the year at the UP and YK sites, and low but dependent on both Ts and θ at the OK site. Annual estimates of soil CO2 flux were 39.9, 23.3, and 21.9 × 103 kg CO2/ha.year at the OK, YK, and UP sites, respectively. All 3 sites were a net sink for CH4, with the highest oxidation rate of –5.1 kg CH4/ha.year at the OK site compared with –1.52 kg CH4/ha.year at the UP site. On a CO2-equivalent basis, the OK site was a greater CH4 sink (–127.3 kg CO2-e/ha.year) than a N2O source (77.5 kg CO2-e/ha.year), demonstrating the potential for soils to oxidise CH4 with forest succession as a possible mitigation strategy for land managers to reduce net emissions.

Nitrogen and carbon cycling in a New Zealand pumice soil under a manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) shrubland

Shrubland communities dominated by manuka (Leptospermum scoparium J. Forst. and G. Forst.) and kanuka (Kunzea ericoides var. ericoides ((A. Rich) J. Thompson) are widespread throughout New Zealand. They frequently colonise disturbed land surfaces and are important for erosion mitigation, and also for their capacity to act as a carbon (C) sink. We here investigate C and nitrogen (N) cycling in 3 stands (~26–56 years old) that had established on a repeatedly burned forest site on a Podzolic Orthic Pumice soil in the Turangi area, central North Island. For comparison, limited measurements of N cycling were also made at other manuka–kanuka sites on non-volcanic soils. Leaf N concentrations at the Turangi site were 11.8–13.9 g/kg, and lower than those at many of the other manuka–kanuka stands. Total annual litterfall and N content increased with stand age, as did total N concentrations in FH material and mineral soil (0–100 mm depth). Total C concentrations in mineral soil did not, however, differ significantly in the 3 stands. Levels of soil microbial C and N, rates of carbon dioxide production, and metabolic coefficients (qCO2 values) suggest C cycling could be fairly rapid at this site. In contrast, rates of net mineral-N and nitrate-N production were low to very low compared with those in similar pumice soils under angiosperm–conifer forests, and in the non-volcanic soils under other manuka–kanuka stands. Low N availability and tight N cycling at the Turangi site are thereby strongly suggested. No definitive explanation for the atypically low N availability at this site is apparent, although the possible effects of previous forest burnings may have been a contributing factor. The continued growth of these shrubs, nevertheless, shows they can compete successfully for the N that does become available through gross N mineralisation in the Turangi ecosystem.

New Zealand Eriophyoidea (Acari: Prostigmata): an update with descriptions of one new genus and six new species

The New Zealand fauna of Eriophyoidea (Acari: Prostigmata) is updated with a checklist. One new genus, six new species, three new combinations, one new record and some new distribution records of eriophyoid mites from New Zealand are described and illustrated, namely Disella rebeeveri sp. nov. on Kunzea ericoides (Myrtaceae); Cecidophyopsis hendersoni (Keifer, 1954), rec. nov. on Yucca glauca and Y. elephantipes (Agavaceae); Nameriophyes sapidae gen. nov. & sp. nov. on Rhopalostylis sapida (Palmae); Eriophyes bennetti sp. nov. on Fuchsia excorticata (Onagraceae); Eriophyes georgeae sp. nov. on Brachyglottis elaeagnifolia (Asteraceae); Aceria flynni sp. nov. on Kunzea ericoides (Myrtaceae); Aculops propinquae (Manson, 1984), comb. nov. on Coprosma propinqua (Rubiaceae); Aculus corynocarpi (Manson, 1984), comb. nov. on Corynocarpus laevigatus (Corynocarpaceae); Aculus heatherae (Manson, 1984), comb. nov. on Raukaua simplex (Araliaceae), Leptospermum scoparium (Myrtaceae) and Syzygium maire (Myrtaceae); Aculus lalithi sp. nov. on Melicope ternate (Rutaceae). A key to the New Zealand species of Eriophyes is provided.

Hybridism in the Kunzea ericoides complex (Myrtaceae): an analysis of artificial crosses

Observations of wild plants and herbarium specimens suggest that hybridism is a feature of the Australasian Kunzea ericoides (Myrtaceae) complex. In this study 73 artificial cross combinations were attempted with New Zealand material of Leptospermum scoparium, five Kunzea species, two varieties and six informally recognised entities within the New Zealand K. ericoides complex. The results of these crosses are documented, and for five hybrids spanning the intergeneric, interspecific and intraspecific crosses attempted, we provide a more detailed assessment based on morphology, molecular (nrDNA and chloroplast) sequence variation, and genomic in situ hybridisation (GISH). This is the first time GISH has been used in the Myrtaceae. Hybrids were easily generated between the New Zealand members of the K. ericoides complex, but not between them and the Australian K. ericoides complex. We were unable to produce hybrids between the New Zealand K. ericoides complex and two more distantly related Australian species, K. baxteri and K. parvifolia. Intergeneric crosses between New Zealand plants of Leptospermum scoparium, Kunzea sinclairii and an informally recognised variant K. aff. ericoides (b) were successfully produced, but failed to flower. The molecular evidence and observations after GISH show that even when low levels of sequence divergence exist, genome differentiation, to different extents, can be observed. The results confirm some suspected New Zealand hybrid complexes. However, while hybrids were easily generated artificially, natural instances of hybridism appear to be largely confined to those habitats significantly disturbed since European settlement of both countries.